HP sold what they called a "personal computer" in the 1960s, well before Apple and Microsoft came around. It wasn't exactly what we consider to be a personal computer nowadays, but MySpace wasn't exactly what we consider social media to be today either. I'm not sure these things happen in discrete steps like you seem to imply. There is a clear continuum. I think it is quite fair to say, for example, that Meta help define its industry like Microsoft and Apple helped define theirs.

There will never be exact replicas of Apple and Microsoft again, but there undoubtedly will be many companies in the future that we will eventually look back upon in the same way.

You are confusing the first personal computer with the rise of personal computing. Inventing a product isn’t very useful if you don’t invent the product market as well.