It seems https://mirrors.fedoraproject.org/metalink?repo=fedora-35&arch=x86_64 is not responding.
On the other hand, 34, 36 and 37 are fine:
Can’t add links for 36 and 37 (limited to two links).
This must have been a temporary hiccup with the mirror manager because right now it’s working fine again (at least for me); I am getting a metalink file when opening https://mirrors.fedoraproject.org/metalink?repo=fedora-35&arch=x86_64
For what it’s worth, Fedora 35 is now end of life. I strongly recommend that you upgrade to Fedora 36 or 37 at your earliest opportunity. Fedora 35 is not going to get any updates at this point, security or otherwise.
Yeah, it was temporary, works now.
Regarding upgrade - I was actually trying to update Fedora 35 so I could do system-upgrade to 36 and 37