Thanks a lot for those precise answers. I was able to find the problem. I made an error when locating Visual C++ 14.28.29213.0 redistributable. In fact i had version 14.0.23026 installed...
After downloading and installing the right version, i can now start ProxHTTPSProxy's PopMenu TLS 1.3 3V3.
One day of head scratching for this error
Plus one hour of research and URL manipulations to get around the Mediafire blocked file
Looking for the right version i did see a 14.29.30139 version :
https://community.pcgamingwiki.com/files/file/2883-microsoft-visual-c-redist-2015-2019-for-windows-xp/
Is it really working ?
I can now try 3V3 on the Athlon XP-M machine where i need it. In the meantime i did install an SSE2 TLS 1.2 version on another PC in the same network, and did configure the Athlon XP machine proxy settings to target this PC. This was working.
Edit : i cannot install Visual C++ 14.28.29213.0 redistributable on this Athlon XP-M machine (SSE compatible). I got this error :
As a side note, a lot of forums posts have lost interest because the files they are pointing to have been deleted, sometimes by antivirus systems, sometimes because the site did close, or other reasons.
It's good when possible to self host, use archive sites for such important and extensive works, and or at least have a local copy.
Thanks a lot for all this very nice work.