There are two aarch64 kernels.
https://archlinuxarm.org/packages/aarch64/linux-aarch64
and
https://archlinuxarm.org/packages/aarch64/linux-rpi
do a
$ uname -a
results should be either
linux-aarch
or
linux-rpi
I believe the linux-aarch kernel is pretty much the mainline kernel compiled for 64 Bit arm and for general 64 Bit usage.
The linux-rpi kernel is the Raspberry Pi Foundation kernel with patches for Arch and is aimed more at the RPi 4 series.
I am guessing you have the linux-aarch kernel. Try swithcing kernels as such:
sudo pacman -R --noconfirm linux-aarch64 uboot-raspberrypi
sudo pacman -Syu --noconfirm linux-rpi raspberrypi-bootloader raspberrypi-firmware
reboot and see if that helps.
Pudge