After paste, i want to change paragraph style changes entire pasted text

I paste a page from google keep (other apps the same problem), to LO writer, when I try to change a paragraph style the entire pasted text all changes. When I ctrl-z to undo all the pasted text is highlighted.

Yes, that’s expected and absolutely normal. It’s a great feature of styles, that changing style changes all places where this style is used (unless it is overridden by manual formatting).

If you only need some local change, you have two options:

  1. Create a new style and apply it where you need. This is a superior way.
  2. Apply manual (direct) formatting, i.e. don’t change style, but instead use Format menu.

The latter looks simpler at first, and great many users only ever use it, and even consider the former way too complex and awkward. However, if you rely on manual formatting, you make your document not structured, and naturally when it comes the time when you could benefit from styled approach, your data is way too fragmented to reformat. It’s already too late, and users usually “confirm” their perception of styles being inconvenient, when actually they made it difficult themselves.

Perhaps I will clarify my problem.
On my tablet, I type a note into Google keep, then I add a scripture from my Bible app, then I type more notes.
Later I go to my desktop, to google keep, select all, copy, and paste into LO writer. Then I select the scripture paragraph to change it to “scripture” paragraph style, which is in my normal template. It changes all the text that I pasted, as if it is a block that cannot be separated, rather than just the section selected.

I have tried all the formatting, paste special, etc, and nothing makes a difference.