I mean, if you're making a fork, don't use the name of the project you're forking. If you fork Firefox and call it Firefox+ for example, Mozilla's legal department will email you, and ask you to stop violating their trademark.
The issue is about downstream source build packages. These packages are not based on any forks. The MultiMC maintainers don't even want source build packages to exist. They insist that distributing binaries built by them is the only way. This essentially contradicts the Apache 2.0 license, which states that distribution of the original work is allowed.
And there's the hostility throughout the conversation from the MultiMC maintainers.
It's because features like Microsoft login require app credentials, and if you build from source, then you don't have these, and thus certain features will not work. Then people come along and ask why X is not working. Well, you installed an unofficial release and only official releases are supported by the devs.
But MultiMC is not a registered trademark, and the mentioned usage of the name "MultiMC" in those AUR packages is merely "required for reasonable and customary use in describing the origin of the Work and reproducing the content of the NOTICE file" which is certainly allowed by the Apache 2.0 License.
They are only describing the source, and all they've done in these AUR packages cannot even be treated as a fork: all they've done is adding several patches to make the source build work.
