The physics engine in Underworld is tied to the frame rate. If your FPS goes too high, Lara might fly off into space or puzzles will break.
Since the game is older, some historical preserves host the original disc images. However, you'll still need to hunt down No-CD patches and widescreen fixes to make it playable. Essential "Solid" Tips for PC: Tomb Raider Underworld Free Download
This is the most reliable route. These versions are frequently updated to run on Windows 10 and 11. It often goes on sale for under $2.00 , which is essentially the price of a candy bar for a full AAA experience. The physics engine in Underworld is tied to the frame rate
This title actually runs beautifully on the Steam Deck if you're looking for a handheld experience. Tomb Raider Underworld Free Download