I'm trying to record my first run of Celeste on my laptop with OBS, but I'm getting insane input lag. Please help

Check your OBS settings. Keep reducing your recording settings until your pc can handle it.

Even 480p, 30fps and lower bitrate (or lower preset) can be a viable recording. Celeste is pixel-based so generally all recordings look good. I record 720p 60fps personally, but that depends on what your pc can handle.

Either way. Just keep changing your settings until you hit something you are satisfied with. As long as the mods can verify your recording, you should be good to go. Worst case scenario, you can just point your phone at your screen and record the game that way.

As someone who regularly submits 480p 30fps videos, the above is true. Recording in lower quality can massively lower the burden on your machine.