Can't install /e/ on CMF 1

[aibd]

This also is expected. You are still not telling us if Windows Device manager sees this as a Problem device in Fastboot mode.

If yes, the problem is Windows and / or your machine.

@astep

I think there is no connection then

Again, if yes …

@aibd

Why does it happen

Windows is inclined to install a basic driver for “normal” activities on the phone. Fastboot mode likely requires a more complex driver. The driver may have a name as “Combination driver” or a name where a different or Google device is mentioned; not a problem.