photo app not responding

The Photos app is part of the system so you'd have to reinstall the system. It's not the app but probably the library.

1 - As a test launch Photos with the Option key held down and create a new, test library.  Import some photos and test to see if the same problem persists. Does it? (This tells us if the problem is limited to your current library or is more wide spread).

Then try opening your original library again.

2 - next, if necessary, log into another vanilla admin user account, Set up users, guests, and groups on Mac,  repeat #2 and see if the problem persists. (This tells us if the problem is limited to your user account or is system wide).

What version of Photos are you running?

Where is the library located? If on an external HD how is that drive formatted and connected to your Mac?

How much free space do you have on your boot drive?

What model and year Mac do you have?

Try the following: as a test launch Photos with the Option key held down and create a new, test library.  Import some photos and test to see if the same problem persists. Does it? (This tells us if the problem is limited to your current library or is more wide spread).

Then try opening your original library again.