Hi, @willmatheson
I tested this on my Mattermost 5.35.2 and verified that normal users can @mention me as the System Administrator as I am listed on the mention list as tested in the Town Square and Off-Topic (since they are the default channels):
When I am being @mentioned in the channel:
- Can you share the screen shots of the behavior you are seeing on your end?
- How did you configure your username on your account?
- Is this also happening to other System Administrator accounts too?