Though this may be not all faces that I need to fix, but at first glance, everything that I use now looks as before the update. I am sure that I will keep adding faces to the lists, because I know that I've missed many of those in a places I do not remember right now. These are the faces I've changed:
(when (>= emacs-major-version 27)
(with-eval-after-load 'org
(dolist (face '(org-block
org-block-begin-line
org-block-end-line
org-level-1))
(set-face-attribute face nil :extend t)))
(with-eval-after-load 'magit
(dolist (face '(magit-diff-hunk-heading
magit-diff-hunk-heading-highlight
magit-diff-hunk-heading-selection
magit-diff-hunk-region
magit-diff-lines-heading
magit-diff-lines-boundary
magit-diff-conflict-heading
magit-diff-added
magit-diff-removed
magit-diff-our
magit-diff-base
magit-diff-their
magit-diff-context
magit-diff-added-highlight
magit-diff-removed-highlight
magit-diff-our-highlight
magit-diff-base-highlight
magit-diff-their-highlight
magit-diff-context-highlight
magit-diff-whitespace-warning
magit-diffstat-added
magit-diffstat-removed
magit-section-heading
magit-section-heading-selection
magit-section-highlight
magit-section-secondary-heading
magit-diff-file-heading
magit-diff-file-heading-highlight
magit-diff-file-heading-selection))
(set-face-attribute face nil :extend t)))
(with-eval-after-load 'ediff
(dolist (face '(ediff-current-diff-A
ediff-current-diff-Ancestor
ediff-current-diff-B
ediff-current-diff-C
ediff-even-diff-A
ediff-even-diff-Ancestor
ediff-even-diff-B
ediff-even-diff-C
ediff-fine-diff-A
ediff-fine-diff-Ancestor
ediff-fine-diff-B
ediff-fine-diff-C
ediff-odd-diff-A
ediff-odd-diff-Ancestor
ediff-odd-diff-B
ediff-odd-diff-C))
(set-face-attribute face nil :extend t)))
(with-eval-after-load 'hl-line
(set-face-attribute 'hl-line nil :extend t)))
This is now a part of my configuration of doom-themes package.
--
Best regards,
Andrey Orst