Yes, you are correct, I made this sound too simple, apologies.
If your FP3 is on official, security updates just ran out for Android 13.
You could manually install community to go where the security updates are if you want to prioritise them, but it was announced that community would not be available forever either once official caught up to newer Android, so then it would mean to manually switch back.
It’s a concern, I agree.
But there are still users with supported phones on Android 12 official out there, so it could be worse for FP3, if that’s any consolation.