Like OWA and Teams chat, Outlook for Windows boasts the ability to add Loop components in messages. The implementation is very similar to OWA, as you’d expect, which means that some of the same shortcomings seen in OWA are in Outlook for Windows. Such is life.
Outlook for Windows has supported Microsoft 365 Groups since 2015. The developers chose a seen/unseen model for Groups, but now Outlook has switched to a read/unread model, meaning that the unread counts for Groups can suddenly seem much higher than before. It’s a one-time change that aligns Outlook desktop with OWA and Outlook Mobile and there’s an easy way to set all unread items to be read. But you might want to tell people that this change is coming!