SharePoint Permissions, but could be me being an idiot...

Hi All,

First of all I think I should state that I'm probably missing something pretty obvious.

What I need to do is make the site "Members" unable to Add Column on a list.  I planned on changing the permission level from Edit to Contribute at the main Members Group Level but I was unable to do that, the option to "Edit User Permissions" under Modify when I select the group wasn't available.

I then broke the inheritance on a list and changed the permission level to Contribute like so:

But my member user can still Add Columns on the list.  Am I just being daft here?

*Edit to add.  Switching to Classic mode this works as expected.  So I guess my question is how do I disable the Add Column button in Modern Lists?

Any help greatly appreciated.

Thanks...

John