I am running nextcloud server at a webspace hosting by Hosteurope (Godaddy) since 5 years. No problems and working for my needs, private usage with family and for synchronisation purposes for 5 or 6 machines I am using at home.
Now I want to move to another provider because Hosteurope becomes complicated and more and more expensive.
Are there any known problems with IONOS webhosting ultimate?
Install yourself on webspace, it was more common in the early days, since there are more and more managed solutions, there is little benefit of the hosting packages. Also installing it on different devices has become a bit easier (NextcloudPi, Docker) and even a few NAS/Router provide such options now.
Webhosting often comes with not obvious limitations and are harder to optimize and debug.