I think you can create a preview rendering for Block and in that code, you can check for the Expired content.
Please refer below posts for creating preview block-
I'll try that, thanks!
Usually when using On-Page Editing, Episerver adds a striped layer to indicate that a block has expired. However, this does not work when the block is placed in the content area of another block. It just looks like normal. Is there a way to get the same confirmation there when a block has expired?
Episerver CMS v11.14.0
Episerver CMS UI 11.23.2