i am pretty new about all this kind of technologies but i want to put some documents (.odt or something like that) online and want to edit these documents from different devices (pc, phone, etc) without having to download/upload all the time.
What kinds of (privacy friendly) programs/apps are used for this?
Only office. Afaik, apple also opened its web version of office apps. I don’t have any proof that they are privacy friendly, but I believe it cannot be worse than Google and Microsoft.
If you’re willing to install Software, OnlyOffice can do that with existing formats quite well (the MS Office compat. is also quite good)
If you’re looking for something on the web, I’d wait for Cryptpad to roll out Word Document support. Currently they’ve deployed this as a beta-feature for users that donated on cryptpad.fr, but I would wager a guess and say this could probably be enabled on other instances too.
If you have a Nextcloud instance in a VPS or local NAS with online access, you can install Collabora: the online LibreOffice. If docx compatibility is important, IIRC you can also self host OnlyOffice this way.