TP-Link Archer MR200 cant update

Hey everybody

I got a used Archer MR200 (eu) V. 1, its a spain version from Amena sim unlocked. I tried to update, but it doesnt work. Over GUI it says 1.0.5 is the newest available, when I click Upgrade it crashes at rebooting, my 4G is gone and Im on the same version. (Hardware reset fixed it)
I tried some .bin over LAN and GUI, I get the message my hardware is not supported.
What can I do to install the latest, unbranded software version? Need to update the modem for DT Germany

Have you searched the forum already?
There are multiple postings about MR200. Please check if you find something useful.

I already looked the Forum, found some interesting in the archives too. I need to flash the firmware with tftp and cut the header as far as I know.
But I have no idea if its the right way, dont want to brick my device. Some sort of how to would be nice.