It says all the right words and has a flashy landing page, but doesn't seem very open or impressive; am I wrong in my assessment?
What is the not-open source software used in OpenDesk? Because your example: cryptepad[2] is GNU Affero General Public License. And diagrams.net might look similar, but also LibreOffice looks similar to MS office.
The Calendar is closed source?
And probably also the e-mail client and contacts list?
It looks like multiple items in deploying the "enterprise edition" have licenses and are actually a closed-source model.
To me this looks like a flashy web page that makes all the right noises about "data sovereignty", etc, but relies (on the actual back-end) on multiple providers who have in fact cut off access to code; they even take pains to say it is "less than x% of code" or "Admin Console container image: 100% closed source", etc.
There are multiple examples on that page.
Then the effort sucks.
From my perspective as a German, this almost looks like a scam. It's a bunch of OSS software rebundled as a package by a company which would like to make money off of support for the software. Which inherently sounds great, except that their only original contribution to the software package is a mid tier project management app.
The vibe I've been getting so far, is that they're trying to resell OSS software and accompanied support, except the underlying software already has great community and commercial support (Nextcloud and Collabora for example) and to make up for that, they're getting the german government to slap a "Made in Germany" label onto the package.
Now they push projects like OpenDesk[1] to fully replace MS Office (365) and OpenCode[2] where they open-source all software that is build with public money.
In my view, this has led to the German economy having more confidence in open source, and that open source can be used and maintained as a model for software over a period of 5-10 or even more years. Instead of buying licences and hoping that the manufacturers will maintain the software for at least 5 years and provide updates. In addition, there is the realisation, not least as a result of the change in the law and the current global political situation, that sovereignty is a very important factor.
[1] https://www.opendesk.eu/en
[2] https://opencode.de/en && https://gitlab.opencode.de/explore