adb sideload lineage.zip yields adb: failed to read command: No error
The solution in this very specific case seems to have been reinstalling the host OS (in my case Windows 10). I suspect it to be a driver issue of some sort as the reinstallation of everything used the exact same setups, files etc. I could guess into some of the multiple DisplayLink-ish software I tried to use for my tablet as secondary USB PC display. (Such as Superbrush, Super Display, VirtualTablet, WiredXDisplay, spacedesk and so on, I tried a few.)
While this is not a direct answer to the question, I hope, it could help other people stuck like me. The exact same procedure led to the desired, previously blocked resullt.
TL;DR:
Try a different host device or new installation (of the host OS) instead of giving up!