Did some digging and it turned out making Arch Linux ARM boot from an SSD is pretty hard. Here, have a guide on how to install EndeavourOS from an Arch Linux ARM micro SD card. It takes max 10 minutes:
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#install arch linux arm on an sd card, then boot it.
#insert USB SSD
su
pacman -S wget git parted core/btrfs-progs dosfstools
git clone https://github.com/endeavouros-arm/image-install.git
cd image-install
./install-image-V2.X.sh #where X is a number.
#do the installation
poweroff
#remove the SD card
#boot USB SSD
su
cd ~
#now run the script in the root home folder.
reboot
#log in as root, do not su
cd /root/install-script/
./endeavour-ARM-install-V2.7.sh #the version might vary
# Enjoy Arch Linux ARM on your SSD!
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thanks to jfabernathy for showing the way
continue on with
https://arm.endeavouros.com/headless-server-install/