Found my GUID! Using this tool: https://www.generalarcade.com/gamepadtool/
It is different than yours.
This is what works for me on my 2600-daptor D9 (purchased in Nov. 2019 with latest firmware v.230204):
03000000d8040000ebf6000011010000,2600-daptor D9,a:b0,leftx:a0,lefty:a1,platform:Linux,
Very nice to be able to use the classic 2600 controllers on the 400 Mini!
Thanks!