When I once wasn’t fast enough to disable syncing to Google after a reinstall I noticed that MyPhoneExplorer is able to distinguish between contacts synced with Google and contacts stored locally on the phone.
3 of my contacts didn’t show on the phone anymore, but MyPhoneExplorer listed them separately as Google contacts. With MyPhoneExplorer I could then copy them back to the phone storage from there and could delete them at Google.
Perhaps you could try that.
Here’s an old thread about this, supposedly there are Apps to do it (which the thread doesn’t name) …
https://forum.fairphone.com/t/how-to-access-my-contacts-from-the-sim-card/19039