I am the System Admin on our 5.35.2 instance of Mattermost. In regular channels, even where I’m a member (e.g. Town Square, or channels I create myself), other people don’t get the hint to tag me when pressing the @ key and have to actually spell out my username, which then does work as a tag - they just don’t have the convenience of picking it from a list.
Regular users don’t get an option to tag the System Admin when pressing @ in regular channels, even when the System Admin is also a member
Steps to reproduce
On 5.35.2, set up a system admin and a regular user, and see if the regular user can @ mention the admin without having to spell out the admin username.
Users should see the system admin as an option when using @ in channels, if the admin is also a channel member
The system admin does not appear as an option when using @ in channels, and users who need to mention the admin are obliged to spell out the username themselves (some might argue this is a feature!)