So that's why MultiMC removed CurseForge support (in commit 0a827ba70e6ef20187f8507a536d54a8441020dc). (The commiter couldn't even bother to include the full explanation in the merge commit. This is why I hate GitHub.)

So scummy of CurseForge. They're also trying to insert ads.^["As we supported Linux, we tried to technically look on how ad monetization would look like on Mac & Linux (something that we didn't yet have the bandwidth to do).", Old API deprecation, Linux and Standalone client FAQ]