Continuing the saga, on Debian Trixie (unstable) it appears openssl 1.0 is totally unavailable as far as I can tell, and replaced by openssl 3. Or if I go back to older versions I can get openssl 1.1, but it still doesn’t have the symbol versioning junk that is expected by something expected by openssl 1.0. Haven’t been able to dig up an old version of the libssl1.0 .deb yet, and trying to do some ugly hacks to make the 1.1 deb function hasn’t succeeded; I’ll keep looking.
Edit: Works fine in wine so far though.