[itsme]

That's what I expected: that it's not your choice how the "share" app list is populated.
On Android it is just overloaded with useless apps that makes it inconvenient to find and select the one I want to use. Not nice, but it works.
On Win10 this mechanism makes the "Share" function completely useless by now. On one of my computers there's only OneNote, which I don't use. One the other computer there's OneNote, the Win10 buit-in e-mail program  that I also don't use and have not set-up and Oxford Dictionary that doesn't make sense in that context. None of the programs that I'd like to use: Notepad, Notepad++, Excel, LibreOffice Calc, Winword, LibreOffice Writer, Thunderbird...
None of the apps offered by the store look promising to me.
Would you be so kind to give me some keywords to search for in the internet, like the mentioned  'intent' for Android? Hopefully I can google some hints what I can do, maybe a way to "register" apps somehow to handle text files.
Thanks in advance.