Linux

Endeavour will tend to be more up to date than Fedora. On the other hand Fedora has more testing before each major release, so some bugs will be caught before those updates are pushed out to you. Endeavour is essentially Arch with a predefined set of packages and its own GUI installer so you're signing on to ride the rolling release ride and accepting the level of instability that comes with.

Whichever you choose I'd think about setting up the system on top of btrfs or another CoW filesystem so you can take proper snapshots before updates, that'll let you roll back to a previous state if something really goes wrong. (And it will while you're learning how to work with Linux.)

When I switched from Debian Sid to Arch I put a bit of time into configuring btrbk and wrote a set of pacman hook scripts that would take system snapshots automatically before pacman updated packages. I found that setup pretty helpful while I was learning Arch, even if it was just to dip into previous versions of files in /etc from before an update to compare with whatever I had at the time.

Endeavour has a pretty healthy community that's happy to help onboard new users while Fedora is generally considered a bit more stable (Linus Torvalds uses it on his work machines) so both choices are pretty solid. I found Arch easier to hack on personally, the packaging and build system are really straightforward and the Arch wiki is fantastically comprehensive.