is there a newer version than 7.9.1 for my Time Capsule

7.9.1......introduced in May 2019 is the most up to date firmware.

Apple has done virtually nothing since that time in the way of any support for the AirPort line. I would not expect them to change their ways.

It is latest and greatest.

To discover the latest.. hold down the option key and click the version number of the firmware.. a list will appear.. as well as an error if there is a later firmware you have not upgraded to.

I have deliberately not upgraded the firmware on the Airport Express. So it gives an error I have ignored.

Not every update is an advance to the latest greatest.. some are downright unreliable.

You can also turn off checking for new firmware.. or on if you happened to turn it off.. that allow the Airport Utility to check apple servers for the latest and occasionally greatest but sometime worse firmware.

I would expect a new firmware about when H3LL freezes over. The Airports have been out of production for nearly 3 years now.. and the last one came out May 2019.. so don't hold your breath.