iCloud password verification fails during new Mac mini setup

I'm struggling to set up a new mac mini.

My Apple ID is set up to an old email address that no longer exists.

I can access my Apple ID on my iPhone, my PC (via itunes) and on my Mac Mini.

My problem is that iClould will not accept my valid password on the new Mac Mini. It tells me that verification has failed - that my password is wrong?

So, I can't get iCloud setup on my Mac Mini - I think I also need iCloud set-up for the Apple Music App and for the App Store to work?

I've also been trying today to set up a Native Instruments MIDI keyboard and software - which has also not worked so far.

I suspect, but am not certain, that I can't set up my Native Instruments hardware and software because my Mac Mini is not letting me install smoothly because I've not completed my basic Mac Set-up by fully integrating with iCloud?

Should I be able to set-up my Native Instruments hardware and software with my Apple ID being functional but not fully set up with iCloud on my Mac Mini?

Has anyone got any ideas that could help?