Apple has updated Catalina 10.15.5 to 10.15.6 and 10.15.7, so you would want to apply those updates as soon as possible to your Macs.
After the Macs have been updated, power off the Time Capsule and leave it off for a few minutes, then power it back up.
On the iMac.......
Hold down the option key on your iMac while you click on the Time Machine "clock" icon at the top of the Mac's screen
Select Verify Backups
The process might take anywhere from a few minutes to an hour or more depending on how much data is stored in the backup on the Time Capsule
Let the process run until it completes, or until you see an error message appear
If an error message appears, post back with the exact text of the message
Perform the same process on your MacBook Pro and post back on your results
On a separate note, the 2012 Time Capsule is now 8+ years old, which is past the normal useful life of the product, so you would not want to store any data on the Time Capsule that you cannot afford to lose, unless you have another backup on another hard drive.
.
