Yeah there was actually a Samsung reuse-for-IoT program for old hardware.

Unfortunately it was really dumb and you could only use your phone for a few usecases blessed by our Samsung overlords. As far as I remember you could use the phone as a light sensor or something which was terrible overkill.

It wasn’t anything like postmarketos. It’s been deprecated or killed off silently too in the last few years.

Unfortunately the S8 are hardly supported by AOSP distros. Lineage only supported the S7, S9 and S10 (the latter two it supports still) but the S8 was never on the radar somehow. Postmarket doesn’t support it either. The only distros I found were a few once-off images (so no updates whatsoever) on XDA-Developers, with lots of things non-working.