How can I stop indexing intellij idea?

Try:

File-> Invalidate Caches / Restart.

I think that this issue happens (at least for me it seems to be the reason) if you start commit and then close the IDE in the middle of the process.

You can stop synchronizing/indexing each time you switch to the IDEA and it's quite useful when dealing with big projects and outside build process which triggers indexing.

Just disable checkbox System Settings -> Synchronize files on frame or editor tab activation.

Make sure you run indexing manually to update hints when needed through Synchronize menu (Cmd-Alt-Y on Mac) or File -> Reload All from Disk to run it manually for IDEA 2020 running under Linux