bookreader
Ok, so I received my new shiny unit today and was able to successfully install OpenWRT with USB stick.
I can bet the reason why it didn't work for you is because the *.itb file you downloaded has the following name:
openwrt-23.05.0-ipq807x-generic-dynalink_dl-wrx36-initramfs-uImage.itb
Whilst the manual says to enter this command:
fw_setenv bootcmd 'usb start && fatload usb 0:1 0x44000000 openwrt-ipq807x-generic-dynalink_dl-wrx36-initramfs-uImage.itb && bootm 0x44000000; bootipq'
Note that the file name they provided does not match the file we downloaded, hence it didn't load the image from the USB stick.
Using this command instead sorted the issue and allowed to boot directly to USB stick:
fw_setenv bootcmd 'usb start && fatload usb 0:1 0x44000000 openwrt-23.05.0-ipq807x-generic-dynalink_dl-wrx36-initramfs-uImage.itb && bootm 0x44000000; bootipq'
The bottom line is that the folks at OpenWRT need to fix their manual and enter the correct file name (or mention the file name can be different from the one we will download).