I haven't tracked it down in 1.1, but in 1.0.2 OpenSSL handles ASCII, UTF-8 and mbcs/ANSI paths explicitly: https://github.com/openssl/openssl/blob/OpenSSL_1_0_2-stable/crypto/bio/bss_file.c#L138

So for 3.6 and later, if we're encoding the paths with fsencode(), it'll be fine, but we could also use utf-8 unconditionally.

Doing a search of the codebase though, there's only the one place that does this and everywhere else just uses fopen() without attempting to decode. I don't think we're exposing many of those publicly though.