Emulators are legally protected and asking for donations is just fine, the fly in the ointment for emulation of modern consoles is that they require firmware and decryption keys extracted from real consoles to actually do their advertised function, the emulator might tell you that it is your responsibility to extract the required files from your own console to protect itself but just like game "backups" it's much easier to download the required files someone else has ripped and uploaded to the internet.

The stupid part was paywalling the latest version of the emulator behind a patreon subscription (it wasn't even effective as anyone could share the latest release) which opened them up to being taken down by nintendo although it was likely they would have been taken down anyway just because the switch 2 was nearing launch and they didn't want switch emulator developers to get started on the switch 2.