Did you run into a boot loop because of some SDMMC controller problem? If yes: this is caused by hardware changes in newer rpi4 and old rootfs images from ALARM which don't support this yet but it's fixed if you update it. To do that, you have to play around with chroot + qemu-user to run a standard "pacman -Syu" on the rpi rootfs before the first boot on the real rpi4. Afterwards it should boot properly on the rpi4.

That being said, if you want to use e.g. the official RPi 7" touch display via DSI, you should also switch from the default upstream kernel to the rpi kernel unless you like to mess around with DTB and debug strange problems.

Using the serial port (I recommend a cp2104 or cp2102N usb-ttl adapter) is extremely helpful.

You'll need to become familiar with u-boot. Then you'll be able to boot this board and any other board with ease.