It’s indeed an OnlyOffice fork. I guess they want to play safe, considering that OO is Russian based.

The intent is to replace MS Office in government use, so it's necessary for the EU to maintain its own codebase. The whole point is reducing government dependence on foreign-controlled software. The only way to accomplish that is to create your own self-controlled fork.

They want me to use a government controlled web based office suite?

It's even a fork of ONLYOFFICE, a Russian developped office suite, might be relevant info for you, if you want baseless paranoia.

It's an open-source codebase, licensed under AGPLv3. That's pretty neat, if you ask me. And being web-based it fills a bit of a different niche, than Libre Office (and I bet it will be pretty compatible). Nobody's gonna stop you from using that, except the same people who would've formerly chained you to MS Office.

Where do you get the government controlled from? It's developed by European companies, not governments and you can selfhost.

You really should read the article before posting comments.