Link: https://nitter.net/TeamFortressS2/status/1745157814295617767
Valve is generally supportive of mods (hell, a Portal 2 mod was just released a few days ago) but it seems like recreating Team Fortress 2 was pushing it… Really sad, honestly. I really hope Valve would just strike a deal with these devs and make it official rather than throw away the insane amount of effort they put into re-building TF2.
Valve seems okay with TF2 mods on the older engine… See https://tf2classic.com/
I feel like the TF2Classic ran into dmca issues earlier in their dev cycle as well.
Edit: yes they did https://twitter.com/tf2classic/status/1436328611485818880