Thank you to everyone for your replies! Funnily enough, this is the first time since I posed the question, I have been able to log back in to respond as Microsoft wouldn’t let me! No surprise there.
I have never been able to resolve this issue on the PC it happened on. The ONLY way I could resolve this was by buying a new PC. When I did that, I made sure I never accepted the backup to One Drive and kept the files I wanted to keep on my hard drive and those I have always had on One Drive have kept there.
Mind you! Every. Single. Time. I save a file on my hard drive it asks me to backup to One Drive. I have to say no every single time. Even when opening a file, One Drive wants access to it.
Frankly, this is disgusting but I have not got into the habit of refusing every time and so far, so good.
Yes, One Drive is great for those files I need to access everywhere but when it comes to everything else, it is invasive and I am not impressed.