Here are some PKGBUILDs!
Note: (Raspberry pi 4 kernel PKGBUILDs forked from https://github.com/moonman/MyPKGBUILDs)
Arch Linux repo: (Built on raspberry pi 4, aarch64)
[raspi_aarch64]
SigLevel = Optional
Server = https://www.gardling.com/my_repo/aarch64/