Oh my god. It was absolutely something simple. For those reading this, notice in my screenshot under Placement, Height the minimum is -262,144. My landscape was below this Z position for some reason, and that’s why it wasn’t painting. I set the minimum to a much lower number and now it’s working fine. , , thank you so much for your help. Posting this and looking at the screenshot finally cracked it open for me. Thanks again!
(If you don’t see Placement and all that good stuff at the bottom, make sure you’ve selected at least one static mesh by clicking on it in the foliage tool.)