I suggest not attempting repairs, it can make the problem worse. Try booting from a current Fedora live desktop image (USB stick, any desktop), and try to mount using:
mount -o ro,rescue=all
If that works, I suggest copying out any important data while you can. Keep it embargoed. The rescue=all mount option disables data checksum verification so the files copied could contain corruption. But it’s sometimes better to have important files such as they are, than not at all.
Next umount the file system and run
btrfs check $DEV
and btrfs check --mode lowmem $DEV
Copy/paste the terminal output here using the preformatted text option. I’ll see if one of the Btrfs developers has a momen to look at it. Most likely these messages will match the kernel messages you posted about bad tree block start. It’s very unexpected that both mirror copies of the tree root, and all the backups, aren’t readable. That’s a lot of problems all at once.
Opening filesystem to check...
checksum verify failed on 808009728 wanted 0x00000000 found 0xca72d647
checksum verify failed on 808009728 wanted 0x780fa0fd found 0x2ce4b8af
checksum verify failed on 808009728 wanted 0x780fa0fd found 0x2ce4b8af
bad tree block 808009728, bytenr mismatch, want=808009728, have=0
Couldn't read tree root
ERROR: cannot open file system
lowmem:
Opening filesystem to check...
checksum verify failed on 808009728 wanted 0x00000000 found 0xca72d647
checksum verify failed on 808009728 wanted 0x780fa0fd found 0x2ce4b8af
checksum verify failed on 808009728 wanted 0x780fa0fd found 0x2ce4b8af
bad tree block 808009728, bytenr mismatch, want=808009728, have=0
Couldn't read tree root
ERROR: cannot open file system