imported videos from google drive to imovie, now some of my scenes have red flickers in them

You didn't mention what remedies that you have unsuccessfully tried.

Try importing into a new project.

Try importing to desktop and from there into iMovie.

Also, you can try deleting/resetting preferences. To delete/reset preferences open iMovie while holding down the Option and Command keys and select to delete preferences in the box that appears. iMovie will open in a new library. Reopen your old library to get back to your projects.  Deleting preferences is a safe procedure that will not cause data loss or disruption to your project.

-- Rich

If the procedures that I suggested previously don't cure it, re-encoding can sometimes work if there is a problem with the clip itself. I realize that you said it didn't cure the issue for you. Not sure what method that you used to re-encode, but one that is handy is to place the clip on your desktop, control-click on it, and then click on Encode Selected Video Files from the drop down menu. That will create an M4v file on your desktop, in addition to your original clip.

-- Rich