aria-haspopup="true" is really intended to signal that an ARIA menu will be opened on activation. as a result, some assistive technologies will announce controls with aria-haspopup="true" as a menu or menu item (e.g. JAWS and NVDA).
In addition, aria-haspopup seems to trigger a bug in Edge/Narrator where the aria-expanded state is not correctly announced at the moment when aria-haspopup is present.
This now makes the dropdown button more like a generic disclosure widget control - see also https://www.w3.org/TR/wai-aria-practices-1.2/examples/disclosure/disclosure-navigation.html01
Closes https://github.com/twbs/bootstrap/issues/33528
(Note this was already done at some early point in v5, with no adverse effect. As this only really affects the documentation/examples/tests, not the actual code, this is a non-breaking change)