Created attachment 219817 [details]
As you can read in the references GitHub issue, this latest version of Nextcloud client needs graphics/qt5-graphicaleffects in order to display its main dialog GUI.
The attached patch should solve this.
A commit references this bug:
Date: Fri Nov 20 21:35:46 UTC 2020
New revision: 555791
Add graphics/qt5-graphicaleffects dependency.
Submitted by: email@example.com