when I press LEFT_ALT to active inventory preview feature, the fps will drop a lot.
using minecraft 1.18.1 and tweakeroo 0.12.0

More information or a repeatable test case? In my test world I drop from like 510 fps to 410 fps when looking at a certain shulker box with a few items inside with the preview. At least some FPS drop is expected since more stuff is being rendered with the preview, and item rendering isn't particularly super fast...

well, my fps is around 100 so when I use this feature, it will drop to about 5 fps...

That still doesn't help me reproduce this issue. Single player or server? What inventory are you looking at, or do you mean when you just hold the key while not looking at any inventory? Are you able to record a video showing this issue? Or can you use the profiler chart in Shift + F3 (navigate it with the numbers listed for each section) to see where the CPU time starts to go when you hold the key?

It's in single player. This does not happen in multiplayer. I just hold the hotkey and look some common blocks, or even look to the air.
After I opened my screen recording programs, the situation got improved magicly.

It must be some kind of interaction with some other mod you have, I don't notice any kind of change in the profiler chart when pressing or releasing the key, even with Sodium and unlimited FPS (ie. pretty low frame times, so even pretty small differences should show up).

emm, I will check this

Please test tweakeroo with c2me. I will check the latest version of c2me soon.
c2me-fabric-mc1.18.1-0.2.0+alpha.6.24-all.jar.txt

The latest build of c2me can also cause this problem.