Unfortunately, this makes things even more difficult and more complicated.
I do not have older backups of an iPhoto Library backed up on a Time Capsule that were made on an older Mac, so I cannot test to see if the steps that I suggest might work. You may want to wait to see if another user will reply before you proceed.
On the MacBook Pro running Monterey......
Open any Finder window and look for the name of the Time Capsule to appear under the "Locations" heading.
If it appears there, click on the Time Capsule and another window will open with the name of the drive on the Time Capsule, which is "Data" by default, unless you have changed the name of the hard drive on the Time Capsule
You may need to click Connect As and enter the administrator password for the Time Capsule
Does "Data" appear?
If no, post back with that info.
If yes, double-click to open Data
After a few seconds, you should see .sparsebundle files for each of the Macs that have backed up to the Time Capsule in the past. The name of the Mac will appear as part of the file name. For example, if the Mac was named "Chang83's iMac", then the file name will look something like "Chang83's iMac.sparsebundle" or Chang83's MacBookAir.sparsebundle".
What are the names of the files that you see?