How does changing Recent Post Display Type affect display and where?
I cleared caches, Ctrl+F5 and never see anything changing when I select posts or topics option.
What does this do and where???
This option doesn't have any relation the the Recent Posts widget. This option is designed for Recent Posts page. The Recent Posts page is this:
It also exists in forum menu and in forum footer.
Ah! Would be great to have seen a small info text on that, I think. You're doing great overall with documentation of your products. I guess I'm just dumb even not being blond 🙁