devicetreedir should be /dtbs/
This is mine(Don’t copy everything, the UUID will be different):
label Archlinux
kernel /vmlinuz-linux-rockchip-bsp5
initrd /initramfs-linux-rockchip-bsp5.img
devicetreedir /dtbs/
fdtoverlays /dtbs/rockchip/overlay/rk3588-uart7-m2.dtbo
append root=UUID=67ad0e7b-3914-48d6-97c2-c48e5e0e405b earlycon=uart8250,mmio32,0xfeb50000 console=ttyFIQ0 console=tty1 consoleblank=0 loglevel=0 panic=10 rootwait rw init=/sbin/init rootfstype=ext4 cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory swapaccount=1 irqchip.gicv3_pseudo_nmi=0 switolb=1 coherent_pool=2M