I looked at it and it’s related to a recent PR (yesterday): A11Y: read who liked/read a post when count clicked (#31549) · discourse/discourse@5312550 · GitHub
A quick test shows the issue is here.
The users array should be tested against its length.
https://github.com/discourse/discourse/blob/main/app/assets/javascripts/discourse/app/components/small-user-list.gjs#L45-L47