I would like to update from 22.03 to 22.03.2. Is it possible to do the update RT-N56U using the Asus Firmware Recovery tool? All the forum threads I've come across and the device page only mention using the tool when switching from the OEM firmware to OpenWrt or debricking the device. There is no documentation about using the tool when OpenWrt is already installed on the device.
sysupgrade with the sysupgrade image would be the recommended approach, this can (but doesn't need to) also retain your configuration over the upgrade.
If you want to use tftp recovery, you will generally need the factory image instead (which might be the sysupgrade image in this case, well, the same type you used initially); usually not the best approach, but possible.
If I understood correctly from the documentation, using anything other than TFTP or the Asus tool will result in a bricked device. There is no factory image for the RT-N56U.
I can't (and won't comment) upon this particular device (never owned one), but if tftp worked in the first place (with 22.03.0), it should with 22.03.2 and upwards, regardless of the question if you currently have the OEM firmware or a previous OpenWrt version installed on the device.
I used the Asus tool to install 22.03.0 from the OEM firmware, as it was much simpler than TFTP. That's why I'm asking if it would work to update from OpenWrt firmware to another.
As @slh already noted - OpenWrt's sysupgrade mechanism is used after converting devices to OpenWrt. That would be the simplest method to upgrade.
If you want to use an un-recomonded procedure to upgrade, you'll have to carefully follow the Wiki and do so at your own risk.
Does updating through the LuCI web UI use sysupgrade? If it does, it does not work on the RT-N56U.
Provide more information and details on what's not working. Do you receive an error message, what happens, etc.?
I see no such thing (unless you're misinterpreting information regarding the initial install from OEM). The Wiki says:
"You can, however, easily update from a stable release to a daily snapshot, but make sure “Keep Settings” checkbox is checked."
This is only possible with a sysupgrade.
That bug thread references initial installation from OEM using the "Factory" image.
Interesting, I would advise asking @tuffalo4sec
If this is the case, I suppose the wiki page could be updated to clarify this and remove any references to upgrading or updating from the "Installation" section. I'd still like to hear from someone who has used an RT-N56U and done a succesful update with sysupgrade.