Yes there are some known issues. If you have a quick glance through the discussions here.. the Time Capsule is now not great as Time Machine target. If you have not had problems up to Big Sur well you are very lucky.
The best suggestion I have seen is to erase the disk.. use the airport utility.. a quick erase is fine. Then start again. No luck we will need to check the network setup so you need to give us a clear picture of network configuration.
What is make and model of modem.. and main router if you have one?
If the Mac uses wifi from TC or another router?
There are multiple things you can try but in the end.. it is more than likely just time to replace TC. If it is 5years or more just bite the bullet and do it.. 3-5years still better to replace as Apple is really moving away from the whole Airport setup and protocol. But if you want to play around we are happy to make further suggestions.
See https://discussions.apple.com/thread/252044155
It goes through some of the details.
One important point is NO ADDED 3rd party security products.
Norton and Sophos have been reported.. but I would not trust any security package. Anti-virus, firewall, etc. And you need to actually remove them.. not just turn them off.