If you install the EPiServer.CMS.UI.* 11.19.1 packages the link in content are 'create new block' stops to work.
Instead of listing all possible blocks or blocks limited by the AllowedTypesAttribute you see nothing - the UI breaks and basically has nothing.
Quick workaround is to create thenew block in the Blocks tab in assets panel.
So stick with EPiServer.CMS.UI.* 11.19.0 packages. A support ticket about this has been created.
I just discovered this same issue myself.
Thank you for creating a ticket. I was just going to do it myself after I discovered downgrading to 11.19.0 fixed it.
Here is the public bug which you should upvote if you are affected: https://world.episerver.com/support/Bug-list/bug/CMS-13807
Just a follow-up, thi sissue has been fixed in the Episerver update 261. The NuGet package containing the fix is EPiServer.CMS.UI 11.19.2.