GNOME Online Accounts uses Owncloud icon for Nextcloud #607
Description
As shown in the screenshot. This is because GOA looks for an icon called goa-account-owncloud even though it corresponds to a Nextcloud account option.
I've reported this bug upstream https://gitlab.gnome.org/GNOME/gnome-control-center/-/issues/1352
A (I would hope) temporary work around for this would be symlinking goa-account-nextcloud to goa-account-owncloud, then adjusting the symlinks again if/when this is fixed upstream.