Hi smittyT,
Congratulations on the new MacBook Pro!
Re: I just migrated all photos from Time Machine.
Am no "Photos" expert, yet your post surely deserves a response.
Wondering which Mac OS version is installed on your new (2022?) MacBook Pro.
It may take some time for your Mac to index all the newly imported Photos so they can all be found when searched for, and opened on demand. It may be a memory intensive task to get all the Photos sorted. I could be wrong; yet if this is the case, leaving the Mac plugged in to power, and turned on overnight, and letting things be for a few days could be the answer.
Other possibilities:
The new Mac's version of Photos may be a lot newer than the Photos (iPhoto?) version in which older photos were originally stored ... maybe an issue (?).
or
If the Photos app is still unresponsive after allowing time, power, and memory for Photos to re-index everything, maybe quitting the Photos app, and restarting the Mac could be enough to put things back in order.
All the best :-)