My MacBook air photos app has been very glitchy

Hi - Also worth restarting your mac in safe mode and then trying.

Then restart normally, and try again.

Safe mode will clear temporary files and caches, and sometimes fixes odd glitches such as this.

Start up your Mac in safe mode – Apple Support (UK)

Also - where is your library stored? If on an external volume what is the format?

Maybe you should try SMC reset

Here’s how to reset the SMC on any Mac notebook model with the Apple T2 Security Chip:

1. Shut down your Mac. 
2. Press and hold the power button for 10 seconds, then release the button. 
3. Wait a few seconds and restart your Mac.
4. If that doesn’t help, shut down your Mac again.
5. Press the right Shift, the left Option key, and the left Control key and hold for 7 seconds. Then, press and hold the power button.
6. 
7. Keep holding down all four keys for another 7 seconds. If your Mac has turned on, it will turn off as you hold down these keys. 
8. Release the keys and wait a few seconds. Then, restart your Macbook.