I have the exact same problem but under Ubuntu 20.04. I run multiple instances of 2.6.4 on Ubuntu 18.04 without problems, but an instance (my first) of 2.7.0 on 20.04 is missing the account button and the activity tab. I installed 2.7.0 from the beta repository, and somehow I am unable to get back to 2.6.4 after removing the beta repository. Maybe we should create an issue on this?
rpm -qi nextcloud-desktop
Name : nextcloud-desktop
Version : 3.0.1
Release : 19.1
Install Date: Tue Sep 1 10:22:53 2020
Group : Productivity/Networking/File-Sharing
Size : 3372956
License : GPL-2.0-or-later AND LGPL-3.0-or-later
Signature : RSA/SHA256, Mon Aug 31 23:33:48 2020, Key ID 62eb1a0917280ddf
Source RPM : nextcloud-desktop-3.0.1-19.1.src.rpm
Build Date : Mon Aug 31 23:32:11 2020
Build Host : goat15
Vendor : obs://build.opensuse.org/network
URL : https://nextcloud.com/
Summary : Nextcloud desktop synchronisation client
The Nextcloud Desktop Client is a tool to synchronise files from
the Nextcloud Server with your computer.
Nextcloud Desktop enables you to connect to your private
Nextcloud Server. With it you can create directories in your home
directory, and keep the contents of those directories synced with
the server. Simply copy a file into the directory and the desktop
synchronisation client does the rest.
Distribution: network / openSUSE_Tumbleweed