Is there are a way to use visibility rules to show a block to any user that does NOT have a specific role(s)?
In rules, you could set up the condition to have a role and then check the "negate" box. I'd don't see that option in visibility conditions for blocks on a layout. it seems that I can only create a positive condition for a role. If a user has a role, show this block.
Otherwise, I feel like I am going to have to create a special role just for users that are supposed to see this block.
Comments
The negate option is available on some conditions. I say file an issue, it may be a simple fix.
I just checked and found the "negate" option on UID and NID visibility rules. I created this issue:
https://github.com/backdrop/backdrop-issues/issues/4689