Yeah that unfortunately seems to be the only option if you don't want to completely reset your device or remove apps one at a time to find the culprit. And there's no guarantee either of those will work anyway.

I've actually found a small number other users reporting a similar issue, though dev responses all seem to believe the issue is likely caused by apps rather than the OS. The fact that the issue is exclusive to GrapheneOS doesn't appear to have swayed them into looking into it unfortunately.

If I were in your position I'd probably use the Auto Reboot setting so at least you don't have to do it manually every day. It reboots after a specified number of hours without an unlock, so it's ideal for when you're asleep.