Valve, for most, doesn’t invoke the sense of “evil” that other gaming companies tend to invoke in the community. They’re not known for squashing games based on their IPs, and even encourage putting up Steam pages for them so they can reach a wider audience.
It’s surprising, then, that the up and coming remake of Portal for the Nintendo 64 (yeah, you heard that right) has been ordered to be taken down by Valve. It’s a confusing situation for those who follow Valve’s modus operandi, but it makes a little more sense once you realize that Nintendo can get a bit litigious. I’m sure Valve doesn't want any more lawsuits to deal with right now.
The reason given for the take down, at least by user @JoeyCheerio on X (formerly Twitter) was that Portal 64 used Nintendo’s proprietary libraries. And when you start to use Nintendo’s stuff without permission, problems start.
Surprisingly, another user made mod, Team Fortress 2: Source 2 has also been ordered taken down by Valve. This one is a direct protection of what, I assume, their plan for that IP will be. So that’s sort of good news, at least in that there is a potential update to Team Fortress 2. One that is almost a decade in the making, since that game has been without an update for quite some time.