MarsSeed [1] filed a deletion request for gtk4-customizable [2]: Unused, broken. Outdated but not even flagged. 0 pkgstats. Name is misleading.
Uses experimentar patch MR has not been accepted by upstream as valid/worthwile, and not been maintained for 1.5+ years. [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/gtk4-customizable/
