How to even install app? Which app? I have una.io app but it is only for this site. How to do it for own site?

you would need to create mobile apps specifically for your UNA site, using code supplied here: https://github.com/unaio/una-mobile-app
Harry Sondre there is an update in Mobile Apps code, perhaps it is timely to update - https://github.com/unaio/una-mobile-app

Alex T⚜️ can perhaps assist.