An interesting customer base might be small communal organisations. At our local scouts troop I had a discussion with a friend, who is also in IT. His idea (not fleshed out) was to provide small local organizations with a stack of already configured open source software to support the typical needs of such organizations (like a wordpress website, a nextcloud for file storage and common calender, limesurvey for surveys and event registration, mailman3 for mailing lists,…). Depending on the needs you could sell the initial setup process (your personal work in setting up and skill transfer) or ongoing support. Though such organizations normally don’t have much money to give away. So probably its not really worth your time financially (though probably really appreciated in the community).

I cannot find callibreoffice. Where can I get it to try? Or do you mean Collabora?

I really need a libreoffice calc on my android phone. Not just opening (where currently only Microsoft Excel on Android works for me) but also editing and saving to my connected nextcloud (where I have also problems with Excel)