Time Capsule will no longer work starting with macOS 27 Golden Gate. It uses a deprecated format for networking (Apple Filing Protocol, AFP), and while that format works with macOS 26 Tahoe, the format will no longer be supported by Apple starting with macOS 27. Apple has exited the networking hardware market. It has been over 7 years since the Time Capsule was last sold by Apple, and that means the product is now considered 'obsolete'. To put it bluntly, your Time Capsule is now essentially a paperweight.
The simplest method to continue using Apple’s Time Machine to back up your Mac(s) is to buy an external drive and connect it to the Mac(s) regularly to back them up (or leave the drive connected to a desktop Mac). External storage is relatively inexpensive, a 1 TB SSD or a 2-4 TB HDD can be purchased for <$200 (prices have gone up significantly in recent months, unfortunately).
To back up your Macs over WiFi, the most straightforward way is to use a network attached storage (NAS) device – essentially a box for hard disks that connects to your network. Ideally, choose one that offers turnkey support for Time Machine out of the box, both Synology (setup instructions) and QNAP (setup instructions) do so. Technically, you can stand up a Time Machine server in other ways (including using a Mac as a TM server), but an NAS is arguably the most straightforward way to set up network Time Machine backups.
Personally, I use a Synology DS223j with a pair of 10 TB HDDs installed to back up 5 Macs in the house with Time Machine (separate shared folder for each Mac sized at ~2.5x the internal storage), with the remaining space used as general file storage for everyone in the house.