Cant go into MASKROM/Cant Flash the first time

[Serverfrog 0]

Hello,
This is my first kind of these Boards (i have multiple Raspberry Pi's etc.) so i wanted to get started on my new Tinker Edge R.
First i waited a bit (because on Amazon it wasn't listed that no power supply is in there) Now i got my MicroSD Card in,googled and found the Rockchip Driver Assistent (that is nowhere to be found on an Asus site, only sketchy looking Websites...), Bridge the Recover Pin,  Connect USB3 Type-C to my PC, insert the Power supply. 
I get an `Rockusb Device` in my Device Tree, i also get in the Tinker_Edge_R-Flash_GUI_V1.0.0-20200326 the Device `TinkerBoard-R USB Devices (maskrom)` but if i try to flash it with either `Tinker_Edge_R-Debian-Stretch-v1.0.13-20210702` or `Tinker_Edge_R-Debian-Buster-v2.0.5-20220217` it tells me to go into MASKROM mode. How can i now find out if its in MASKROM mode? (some LED, output on HDMI, or something) because as far as i understood (if not the Documentation is wrong, there are some typos already in there) i did everything correctly. Is my device DOA?

Thank you for your help.