I am a happy user of yantar92/org's feature/org-fold branch because of its noticeable performance boost with big org files, however I just noticed that org-appear doesn't work with it.
"doesn't work" here means that after I enable org-appear-mode and place cursor over word surrounded by some org-mode emphasis, they aren't revealed, they stay hidden.
When I switch to normal org-mode, issue is gone and org-appear works as intended, so I am confident to say that the issue must be either in the feature/org-fold branch itself or in theory issue could have been introduced to org-mode somewhere after 6b83c6e4ea, because that's the current version of vanilla org-mode used in doom and org-appear works fine with it.
I tested this on stable emacs 27 and vanilla doom emacs profile.