You can run parts of an open source kernel and maybe open source user space. But forget about fully open drivers (binary blobs rule), especially remember resident platform blobs like Intel ME. The remaining exceptions are librem and some hacked thinkpads or chromebooks equipped with coreboot.

And let's not ignore the fact that most cellphones are locked up or have hardware without sane drivers, only ones provided in binary form. Not to mention the kernel running on the DSP to handle modem. Or other things.

Even higher level, just Android, try running its applications without Google proprietary services. While there is a reverse engineered version, it always plays catch up...