Sorting by "Sender" is worded a bit unclear tbh, "Sender name" and "Sender address" would be better in order to understand the intended behavior.So, not sure if a bug came up from an update recently but noticing weird behavior. When I try to sort by sender it no longer does so by display name but instead email addresses only making them hard to readily identify.
Even worse, after setting this sort mode going back to unread retains this - display names don't come back.
Updated 7/2/22 1:49AM
Other than that, I can confirm that in 1.929a (GitHub) too, the behavior is as you describe it. Whether that was different in earlier versions or not, I cannot confirm as I never use that feature.
While I was looking at my version no. under "about" I noticed something. Under "Contributors", the Finnish translation misses the term "translation". Same with Portuguese. That's not a real issue, but it's probably best for each line to have the same wording and offer the same level of information.