FP3: manually upgrade from 1.5. q dev to 1.4. r

[AnotherElk]

Why from 1.5-q to 1.4-r?
Anyway …

@steviexo

First: is it possible or not to change the branch from dev to stable

Possible.

@steviexo

maybe even without data loss?

No.

@steviexo

If so, what is exactly the criteria to change it?

You do a new install including a data wipe.

@steviexo

Second: as I didnt find a clear answer to my first message I decided to manually upgrade via adb sideload with the e/ recovery. I get the message that signature verification failed, do I want to install anyways, I choose yes and then run into ‘error 21’ and ‘E:Failed to find update binary META-INF/com/google/android/update-binary’. I dont get what the problem is

Most likely you are using an install file which is not for installing via ADB sideload.
The install files from the download pages currently match the instructions given here … https://doc.e.foundation/devices/FP3/install.

You can get download links for install files suitable for ADB sideload from https://ota.ecloud.global/api/v1/FP3/stable or https://ota.ecloud.global/api/v1/FP3/dev (see the “url:” lines respectively).