Not technically a remaster, but mods for Minecraft that drastically affect performance but not gameplay have been a thing for quite a while
I don’t know if fan stuff counts, but Kaze Emanuar went through Super Mario 64’s decompiled code and did a lot of optimization that resulted in it running significantly faster on original hardware. I don’t remember what the performance boost was, but it was significant.
Edit: oh yeah, I think I remember reading that the Crysis remaster runs a lot better than the original at comparable graphics settings on modern hardware. Iirc it’s because the original game was created when dual-core PCs were still brand new and low-level graphics APIs like Vulkan weren’t even conceived of yet. As such, the game was mainly optimized for single-threaded performance and the CPU was having to do a lot of stuff that the GPU can do now.
Openmw is a cımmunity made open source engine replacement for morrowind, it does run better on modern hardware
Remasters are often cheap upscaling, so idk. Usually if they put enough work into a game, they call it a full remake. If you’re using the same hardware for a game from the 00s that was remastered a couple years ago, you’re going to need different hardware. A remaster is usually done to exploit new hardware capabilities.
That being said, maybe Shadow of the Colossus or Okami
It’s blizzard, but the diablo 2 remaster runs so much better than the original which was resolution locked to 800x600 and 15fps, they could have kept the same graphics and that would have been enough of an upgrade
The Brood War remaster was actually pretty good, too. It was the last Blizzard product I bought.
Not exactly a fair answer but Red Dead Redemption 1 remastered runs a lot better (60fps) on PS5 than playing the PS3 version via PSN streaming
