TypeError: Argument 1 passed to craft\services\Fields::getGroupById() must be of the type integer, null given When I go to control panel > Settings > Fields, I get a page that throws TypeError: Argument 1 passed to craft\services\Fields::getGroupById() must be of the type integer, null given

This is identical to the issue described here: https://github.com/craftcms/cms/issues/3561

Any ideas as to what might be causing this issue?
This could be due to an issue with your project-config being out of sync somehow. You could try the new ./craft project-config/rebuild console command that's just been added to Craft and see if that gets you back on track.