iMac Fusion Drive corrupted

Mac Fusion Drive (Late 2015) is corrupted.

I ran into problems yesterday whilst using Final Cut. Seems like my computer was very low on storage and suddenly everything stopped working properly. I have freed up a lot of space but the problems persist. I started up in safe mode and ran First Aid which failed with lots of errors on the Macintosh HD - Data volume like ‚error- file xxx beyond the end of the dstream 0’and ‚mismatch between extenders and calculated fsroot’. I guess the hard drive is corrupted.

I thought I would use my Time Machine to restore the system. When I select my external Backups volume as the restore source it asks me to select a Backup. However for the latest version suggested to me is from 2024, which is weird since I have my Time Machine volume plugged in most of the time. Also it here says restore from Macintosh HD on my iMac, not curiously enough from my external volume. There are lots of recent backups from Macintosh HD - Data from my iMac but that requires me to reinstall Mac OS and it will only allow me to install it onto my external drive. Any suggestions how to proceed?

I don‘t particularly want to revert back to 2024. Now when I boot up the Mac I cannot even open Finder so there is no chance of transferring any important data to an external volume.