AR300M uboot fails

i tried according to the tutorial to unbrick the 300m via uboot using all available bin-files.
On each attempt the answer via uboot-Website is

Something went wrong during update Probably you have chosen wrong file (too big or too small) or you were trying to update ART on device with unknown FLASH type (and size) which is not allowed. Please, try again or contact with the author of this modification. You can also get more information during update in U-Boot console.

How can i access the uboot console?

Thank you

PS The s/n is fbb10d28178d04b6

Are you upgrading the firmware or uboot itself?

If you upgrade uboot, you need to go and upgrade the uboot from uboot-for-qca95xx/bin at master · gl-inet/uboot-for-qca95xx · GitHub

If you are upgrading firmware, pls let me know which firmware you are upgrading.
But maybe you can upgrade uboot first.

Hello and thank you
I tried openwrt-ar300m-3.215-0921-1663732325.bin