library versions: OpenSSL 1.1.1b, LZO 2.10

openvpn --show-digests
MD5 128 bit digest size
MD5 128 bit digest size
SHA1 160 bit digest size
SHA1 160 bit digest size
MDC2 128 bit digest size
MDC2 128 bit digest size
MD5-SHA1 288 bit digest size
SHA1 160 bit digest size
RIPEMD160 160 bit digest size
RIPEMD160 160 bit digest size
MD4 128 bit digest size
MD4 128 bit digest size
SHA256 256 bit digest size
SHA384 384 bit digest size
SHA512 512 bit digest size
SHA224 224 bit digest size
SHA256 256 bit digest size
SHA384 384 bit digest size
SHA512 512 bit digest size
SHA224 224 bit digest size
whirlpool 512 bit digest size
BLAKE2b512 512 bit digest size
BLAKE2s256 256 bit digest size
SHA512-224 224 bit digest size
SHA512-256 256 bit digest size
SHA3-224 224 bit digest size
SHA3-256 256 bit digest size
SHA3-384 384 bit digest size
SHA3-512 512 bit digest size
SHAKE128 128 bit digest size
SHAKE256 256 bit digest size
SHA3-224 224 bit digest size
SHA3-256 256 bit digest size
SHA3-384 384 bit digest size
SHA3-512 512 bit digest size
SM3 256 bit digest size
SM3 256 bit digest size
SHA512-224 224 bit digest size
SHA512-256 256 bit digest size

openvpn --show-ciphers
AES-128-CBC  (128 bit key, 128 bit block)
AES-128-CFB  (128 bit key, 128 bit block, TLS client/server mode only)
AES-128-CFB1  (128 bit key, 128 bit block, TLS client/server mode only)
AES-128-CFB8  (128 bit key, 128 bit block, TLS client/server mode only)
AES-128-GCM  (128 bit key, 128 bit block, TLS client/server mode only)
AES-128-OFB  (128 bit key, 128 bit block, TLS client/server mode only)
AES-192-CBC  (192 bit key, 128 bit block)
AES-192-CFB  (192 bit key, 128 bit block, TLS client/server mode only)
AES-192-CFB1  (192 bit key, 128 bit block, TLS client/server mode only)
AES-192-CFB8  (192 bit key, 128 bit block, TLS client/server mode only)
AES-192-GCM  (192 bit key, 128 bit block, TLS client/server mode only)
AES-192-OFB  (192 bit key, 128 bit block, TLS client/server mode only)
AES-256-CBC  (256 bit key, 128 bit block)
AES-256-CFB  (256 bit key, 128 bit block, TLS client/server mode only)
AES-256-CFB1  (256 bit key, 128 bit block, TLS client/server mode only)
AES-256-CFB8  (256 bit key, 128 bit block, TLS client/server mode only)
AES-256-GCM  (256 bit key, 128 bit block, TLS client/server mode only)
AES-256-OFB  (256 bit key, 128 bit block, TLS client/server mode only)
ARIA-128-CBC  (128 bit key, 128 bit block)
ARIA-128-CFB  (128 bit key, 128 bit block, TLS client/server mode only)
ARIA-128-CFB1  (128 bit key, 128 bit block, TLS client/server mode only)
ARIA-128-CFB8  (128 bit key, 128 bit block, TLS client/server mode only)
ARIA-128-OFB  (128 bit key, 128 bit block, TLS client/server mode only)
ARIA-192-CBC  (192 bit key, 128 bit block)
ARIA-192-CFB  (192 bit key, 128 bit block, TLS client/server mode only)
ARIA-192-CFB1  (192 bit key, 128 bit block, TLS client/server mode only)
ARIA-192-CFB8  (192 bit key, 128 bit block, TLS client/server mode only)
ARIA-192-OFB  (192 bit key, 128 bit block, TLS client/server mode only)
ARIA-256-CBC  (256 bit key, 128 bit block)
ARIA-256-CFB  (256 bit key, 128 bit block, TLS client/server mode only)
ARIA-256-CFB1  (256 bit key, 128 bit block, TLS client/server mode only)
ARIA-256-CFB8  (256 bit key, 128 bit block, TLS client/server mode only)
ARIA-256-OFB  (256 bit key, 128 bit block, TLS client/server mode only)
CAMELLIA-128-CBC  (128 bit key, 128 bit block)
CAMELLIA-128-CFB  (128 bit key, 128 bit block, TLS client/server mode only)
CAMELLIA-128-CFB1  (128 bit key, 128 bit block, TLS client/server mode only)
CAMELLIA-128-CFB8  (128 bit key, 128 bit block, TLS client/server mode only)
CAMELLIA-128-OFB  (128 bit key, 128 bit block, TLS client/server mode only)
CAMELLIA-192-CBC  (192 bit key, 128 bit block)
CAMELLIA-192-CFB  (192 bit key, 128 bit block, TLS client/server mode only)
CAMELLIA-192-CFB1  (192 bit key, 128 bit block, TLS client/server mode only)
CAMELLIA-192-CFB8  (192 bit key, 128 bit block, TLS client/server mode only)
CAMELLIA-192-OFB  (192 bit key, 128 bit block, TLS client/server mode only)
CAMELLIA-256-CBC  (256 bit key, 128 bit block)
CAMELLIA-256-CFB  (256 bit key, 128 bit block, TLS client/server mode only)
CAMELLIA-256-CFB1  (256 bit key, 128 bit block, TLS client/server mode only)
CAMELLIA-256-CFB8  (256 bit key, 128 bit block, TLS client/server mode only)
CAMELLIA-256-OFB  (256 bit key, 128 bit block, TLS client/server mode only)
CHACHA20-POLY1305  (256 bit key, stream cipher, TLS client/server mode only)
SEED-CBC  (128 bit key, 128 bit block)
SEED-CFB  (128 bit key, 128 bit block, TLS client/server mode only)
SEED-OFB  (128 bit key, 128 bit block, TLS client/server mode only)
SM4-CBC  (128 bit key, 128 bit block)
SM4-CFB  (128 bit key, 128 bit block, TLS client/server mode only)
SM4-OFB  (128 bit key, 128 bit block, TLS client/server mode only)

The following ciphers have a block size of less than 128 bits,
and are therefore deprecated.  Do not use unless you have to.

BF-CBC  (128 bit key by default, 64 bit block)
BF-CFB  (128 bit key by default, 64 bit block, TLS client/server mode only)
BF-OFB  (128 bit key by default, 64 bit block, TLS client/server mode only)
CAST5-CBC  (128 bit key by default, 64 bit block)
CAST5-CFB  (128 bit key by default, 64 bit block, TLS client/server mode only)
CAST5-OFB  (128 bit key by default, 64 bit block, TLS client/server mode only)
DES-CBC  (64 bit key, 64 bit block)
DES-CFB  (64 bit key, 64 bit block, TLS client/server mode only)
DES-CFB1  (64 bit key, 64 bit block, TLS client/server mode only)
DES-CFB8  (64 bit key, 64 bit block, TLS client/server mode only)
DES-EDE-CBC  (128 bit key, 64 bit block)
DES-EDE-CFB  (128 bit key, 64 bit block, TLS client/server mode only)
DES-EDE-OFB  (128 bit key, 64 bit block, TLS client/server mode only)
DES-EDE3-CBC  (192 bit key, 64 bit block)
DES-EDE3-CFB  (192 bit key, 64 bit block, TLS client/server mode only)
DES-EDE3-CFB1  (192 bit key, 64 bit block, TLS client/server mode only)
DES-EDE3-CFB8  (192 bit key, 64 bit block, TLS client/server mode only)
DES-EDE3-OFB  (192 bit key, 64 bit block, TLS client/server mode only)
DES-OFB  (64 bit key, 64 bit block, TLS client/server mode only)
DESX-CBC  (192 bit key, 64 bit block)
IDEA-CBC  (128 bit key, 64 bit block)
IDEA-CFB  (128 bit key, 64 bit block, TLS client/server mode only)
IDEA-OFB  (128 bit key, 64 bit block, TLS client/server mode only)
RC2-40-CBC  (40 bit key by default, 64 bit block)
RC2-64-CBC  (64 bit key by default, 64 bit block)
RC2-CBC  (128 bit key by default, 64 bit block)
RC2-CFB  (128 bit key by default, 64 bit block, TLS client/server mode only)
RC2-OFB  (128 bit key by default, 64 bit block, TLS client/server mode only

openvpn --show-engines
Sorry, OpenSSL hardware crypto engine functionality is not available.

openvpn --show-tls
Available TLS Ciphers, listed in order of preference:
For TLS 1.3 and newer (--tls-ciphersuites):
TLS_AES_256_GCM_SHA384
TLS_CHACHA20_POLY1305_SHA256
TLS_AES_128_GCM_SHA256

For TLS 1.2 and older (--tls-cipher):
TLS-ECDHE-ECDSA-WITH-AES-256-GCM-SHA384
TLS-ECDHE-RSA-WITH-AES-256-GCM-SHA384
TLS-DHE-RSA-WITH-AES-256-GCM-SHA384
TLS-ECDHE-ECDSA-WITH-CHACHA20-POLY1305-SHA256
TLS-ECDHE-RSA-WITH-CHACHA20-POLY1305-SHA256
TLS-DHE-RSA-WITH-CHACHA20-POLY1305-SHA256
TLS-ECDHE-ECDSA-WITH-AES-128-GCM-SHA256
TLS-ECDHE-RSA-WITH-AES-128-GCM-SHA256
TLS-DHE-RSA-WITH-AES-128-GCM-SHA256
TLS-ECDHE-ECDSA-WITH-AES-256-CBC-SHA384
TLS-ECDHE-RSA-WITH-AES-256-CBC-SHA384
TLS-DHE-RSA-WITH-AES-256-CBC-SHA256
TLS-ECDHE-ECDSA-WITH-AES-128-CBC-SHA256
TLS-ECDHE-RSA-WITH-AES-128-CBC-SHA256
TLS-DHE-RSA-WITH-AES-128-CBC-SHA256
TLS-ECDHE-ECDSA-WITH-AES-256-CBC-SHA
TLS-ECDHE-RSA-WITH-AES-256-CBC-SHA
TLS-DHE-RSA-WITH-AES-256-CBC-SHA
TLS-ECDHE-ECDSA-WITH-AES-128-CBC-SHA
TLS-ECDHE-RSA-WITH-AES-128-CBC-SHA
TLS-DHE-RSA-WITH-AES-128-CBC-SHA
Be aware that that whether a cipher suite in this list can actually work
depends on the specific setup of both peers. See the man page entries of
--tls-cipher and --show-tls for more details.