Workarounds

MacOS

MacOS-specific fixes:

UK Keyboard Hash Symbol: The # character is typed with Opt+3 on UK keyboards, which conflicts with Doom's workspace shortcuts. Re-bind this in insert mode only.
Man-mode: BSD sed doesn't work with Man-mode; use GNU gsed from Homebrew.
Eshell bash-completion: MacOS ships an outdated bash, so point bash-completion at Homebrew's version instead. The path doesn't exist on Linux, so it's guarded here rather than in modules/shell.org.

(when (featurep :system 'macos)
  (map! :i "M-3" #'(lambda () (interactive) (insert "#")))
  (setq Man-sed-command "gsed")

  (after! bash-completion
    (setq bash-completion-prog "/opt/homebrew/bin/bash")))