Stuck on set up. icloud terms and conditions have changed.

I have a late 2014 mac mini and have kept it at the last BigSur os and been having trouble with software I recently purchased fettin error messages and quitting, even though it should be compatible as I checked before I bought it. I've been in contact with the company and nothing has worked. The last thing they suggested was updating so Mojave was already downloaded I just never installed. Last night I installed it and when it was finished I had to go through the set up process, I put in my apple ID password and then it took me to an apple ID security or something like that, I couldn't take screen shots so I do t remember exactly what it said. I put in my password again and I get a red message saying icloud terms and conditions have change. I can't do anything else, I can't hit back and there's no skip. I tried restarting and there's no way to restart. I googled how to do it from the keyboard and that didn't work. I looked up if anyone else had the problem at start up and there were no answers on ghe threads I saw, people that answered thought they were talking about signing into icloud. I just wound up shutting it down with the power button. I haven't started it up again because I was so frustrated.

So, I can't even login to my Mac because it won't let me past that ID security that says icloud terms and conditions have changed. Does anyone know what I can do about it?