For some reasons, my framerate in this game is very unstable. It starts at 60fps but quickly goes to 40 or 30fps most of the time, and worst sometimes. I do not know why, I tried turning V-Sync On and Off, tried turning off every graphic setting one by one but nothing works. It's not a pleasant experience.

When I go to the menu and resume the game, the framerate resets to 60fps but quicky goes down to what I said earlier.

Any idea why?

What's your OS and are you using D3D or 3DFX mode?

I'm on Windows 10, and I am using the 3DFX mode as advised by other players.

Hmm it should work just fine. I'm using 3DFX mode on Win 10 too and don't have any problems with low fps. Which refresh rate have you selected in the "nglide_config" and can you select Vulkan for Video backend (GPU that supports it required)?

My refresh rate in nglide was By App, I will try setting it to 60fps.
I have an RTX 3070 so yes as far as I know it supports Vulkan

Also try setting v-sync on/off.
If that doesn't help try dgVoodoo 2 instead of nGlide, it has both D3D and Glide support.

I tried the Vuikan renderer available in the nglide_config (didn't know it was an option, been so long since I last used Nglide) and it works.

Limiting my framerate makes my character move in one direction non-stop for some reasons, so I keep it by default. Only downside of this is some subtitles going out as fast as they appear, which doesn't seem to be the case for important dialogs so it's just a minor problem.

Thanks for the help everyone!