The project's FAQ are kinda enlightening: https://github.com/Euro-Office#faq

Your question is somewhat answered there: "What is Euro-Office?", "How does Euro-Office compare to IONOS Workspace, office.eu, the Proton productivity suite, Nextcloud Hub or XWiki?"

However especially "Why was a new office suite needed" is telling.

True EU sovereignty spells: the only requirement is, it must work "greatly" with MS. Oh well, in the past libreoffice and the likes mostly chose open formats as their reason.

If EU sovereignty means simply being a rip off, you get into trouble my friends. This is Chinas business and doesn't spell innovation nor does it mean optimism for the future.

> but developed to be [...] integrated in another product that handles documents, for example a file sharing solution, an online wiki, a project management tool and so on

It looks like it only provides the document editing part and you need an app around it to actually open the document from a filesystem and provide its content to this editing interface, and take the output and save it back to the filesystem? (Filesystem, or whatever persistent storage medium)

It's a WOPI app. Designed for embedding microsoft 365 office app in other web apps, but other people implement it. There's callabria, and this.

You'd use it to connect nextcloud to one of these providers. Probably some other enterprise apps I don't know about can use it to edit documents.

VS Code is built on top of the general-purpose Monaco editor component that's used by a bunch of other projects. This thing is basically meant to be the Monaco of rich-text.

When they don't even bother to make a proper example screenshot for their headline image, it's hard to think of it as quality software.

My impression is that FOSS people don't use Office software very much. So are they fit to develop Office software? You need to use something extensively yourself, or do careful and proper back-and-forth with real users if you want to make a quality product.