Regarding your question, you can just clone the package's git URL or download the PKGBUILD
file directly, make your edit and run makepkg
or makepkg -sirc
as the wiki suggests to produce the package and install it.
You can also install the package tar with pacman -U
.
Relevant Arch wiki pages:
https://wiki.archlinux.org/title/Arch_build_system
https://wiki.archlinux.org/title/Arch_User_Repository
But looking at the comments it seems you are using an AUR helper that has a cache you might want to clear as the git repo for that package has an unstaged change for the license file for some reason (or you reset that file so git doesn't complain when pulling).
Edit: I see you figured it out already.
KDE for its Wayland performance and features and occasionally I switch to hyprland if I need a more focused work environment.
In the past I used Cinnamon but it became ever more buggier on Arch and due to lack of Wayland support still it was a dead end anyway.