In that case hardware wise you are out of options. With the Librem 5 you get the closest. There you only have the CPU Microcode, Wifi and Bluetooth firmware, and the cellular modem & GNSS firmware.
Software wise you have quite a few options, albeit few are usable as daily drivers.
- Android drops out because it requires hardware with proprietary HAL. You would have to rewrite huge parts of the OS so that it runs without them.
- Postmarket OS is your best bet for a somewhat usable experience
- Many open source systems run, but calls are difficult to setup and partly unreliable.
- Pure OS should fit your goal best, Mobian second.
With a Droid 4 and Maemo Leste you can also get quite close but have no camera.


There are big differences, Heroic present the gog library in a nice way and supports convenience features like cloud saves (must have with big screen at home and remote gaming on Laptop) as well as gametime tracking, some achievements (dont care about those).
Its far more convenient than Lutris for GoG and of course you can easily backup your Games.