Nice watch you got there.
It'd be a shame if someone installed Linux on it.
(Me, testing out AsteroidOS, on a secondhand TicWatch.)
It turns out that @AsteroidOS is here!
Installing AsteroidOS was very easy indeed.
Like, not even really a project.
And now it is talking to Android (I have not tried it with postmarketOS yet :)), via AsteroidOSSync:
https://f-droid.org/packages/org.asteroidos.sync/
It took about 10 minutes to go from "opening the package from eBay" to "Linux running on my watch, talking to my smartphone".
Nice :)