How to resolve 'This update cannot be installed' error on iPhone 8?

Hi, I have this problem that I can't solve. I had an iPhone 8, that was off for like six months. Before I stopped using it, I didn't delete anything from that device. Today, I turned it on, it was working normally, everything was okay, but I had to delete everything, so my friend could use it. So I did it. And now we have this issue. The phone want's us to install a new update for software- I think. But iPhone 8 shouldn't have any new updates. But without it, it isn't going to work. We can't skip this installation to "get into" the phone. But we can't also install it because it's always saying that "this update cannot be installed". I don't know what to do and where is the problem. (Also English isn't my first language so I hope that you can understand what I was trying to say)

[Re-Titled by Moderator]

Original Title: iPhone 8 actualisations