Previously, placing an empty #+TAGS: in a file would override org-file-tags for the file. In 9.4, an empty #+TAGS: is ignored and org-file-tags is used.
The relevant code in org.el: (setq org-current-tag-alist (org--tag-add-to-alist org-tag-persistent-alist (let ((tags (mapconcat #'identity (cdr (assoc "TAGS" alist)) "\n"))) (if (org-string-nw-p tags) (org-tag-string-to-alist tags) org-tag-alist)))) This regression is undesirable because I have a set of common org-file-tags for most files, but one particular file where automatically detecting the existing tags in the file works better (the default behavior when org-current-tag-alist is empty). Emacs : GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.22, cairo version 1.17.3) of 2020-08-28 Package: Org mode version 9.4 (9.4-elpaplus @ /home/ionasal/.emacs.d/elpa/org-plus-contrib-20200914/)