When I Started Up Minecraft On Forge 1.17.1 With The Immersive Engineering Mod The Game INSTANTLY Crashes! (Probably Because There's No 1.17.1 Download)

Yeah. 1.17 is not supported. We never released a version for it. IE is only available for 1.16.5 and 1.18.1.

If you somehow got a 1.17 file, you probably downloaded malware. You should get rid of that.