Ubuntu client 3.5.1: Could not connect to unix socket

Linux Mint 20 with NC desktop client 3.5.1 and nemo-nextcloud:

After starting nemo on command line with

sudo -u username nemo

is producing a lot of error messages permanently:

Could not connect to unix socket /tmp/runtime-username/Nextcloud/socket. [Errno 2] Datei oder Verzeichnis nicht gefunden

How to prevent it please?