After a tiny bit more research, it looks like for the Portal Demake, Valve did not even actually issue a Cease and Desist, they actually just heavily recommended the project be cancelled /out of fear of the devs being fucked by the far, far more absurdly litigious Nintendo/.
While I think Nintendo’s actually legal argument in that, which would basically be that a whole art style from the lower res and lower poly graphics constitutes essentially their brand … I think this is bullshit and legally dubious, but of course Nintendo has faaaar more money to throw at lawyers than some random indie dev, so theyd likely have their lives ruined one way of another.