@stevenmayjr it should work out of the box if the BuddyPress activity Post field is actually a custom post type, which, from my tests, is not. So it will not work, for the moment. I will put this at the roadmap of this plugin features in order for our dev team to take a look if it’s possible, but I can’t give a date for that now.
Anyway, every time You need to configure simple-tags for a custom type (if available) just go to Tools > Auto Terms and configure it.
If you have a minute, and haven’t done so, please leave a review. It’s what keeps support going. Thank you ??https://www.ads-software.com/support/plugin/simple-tags/reviews/#new-post