This iPhone cannot be used because the required software is not installed.

This is the first time I've seen this error message reported here.

Who or which company replaced your iPhone screen?

I would take it back to the company that did the screen replacement and have them fix it.

A lot of other people here have had this problem? I'm a regular participant here and this is the first time I've seen this reported. I'm not saying this has never been reported by anyone else here in the past, but that does not mean a lot of people as in a very large number of people have had this problem. Certainly not anyone who hasn't opened their iPhone themselves or had a 3rd party do it.

Can you provide a link to the thread here where a lot of other people have reported the same?

There were two people in each thread reporting this problem - all Windows users. Sorry, but my definition of 4 people out of millions of iPhone users does not equate to "a lot" and both threads you provided have been archived since they are quite old.

And there were answers provided on how to fix this, which made up most of the posts in the first thread.

Flea market? Assuming this thread is not a joke, where do you see this message... on your phone, on your computer, from iTunes? We need more info to help.

So, did you reinstall iTunes as suggested in the other threads?

You seriously had someone at a flea market replace your screen?