iMessage pop ups interference

I am having this issue which has been posted before however wasn't resolved it seems. Can anyone help?

Below Ive cc'd part of a previous post as it sums it up far better than I can explain but essentially I am having the same issue. I don't believe the issue is my keychain since everything else seems to work without these annoying pop ups.

In general iCloud seems always to be involved in these "interfering" and repeated prompts from Apple and if you are signed out - for reasons below- they seem to get worse. In other words it seems that a normal, hassle free, day to day usage of apple products becomes more problematic when you don't wish to use the iCloud. It shouldn't be his way because its forcing you to sign in when you would prefer not to.

Sorry for the preamble however every time I start up my new MBP I am asked to sign in to iMessage (actually called Messages on the Mac, but well done Apple for creating an incorrect login screen as well as a non-essential app I can't delete).

I have never logged in to Messages. I never want to log in to Messages. I don't know anyone I would contact via Messages.

Please can someone tell me how to stop these messages? I have to quit the screen 3 times every time I boot up my computer because it appears at 5 minute intervals. I can't access the app Preferences tab because I don't have, nor want to have, this app set up on my computer. I have switched off the 'handover' option under General in System Preferences.

If I need to do something in Terminal, could someone give me the steps, please? I have deleted things before but I'm not confident I'll know what I'm looking for or what the search term(s) should be.

Thanks in advance for any help you can give.