The interesting thing is that the author has been inactive for long enough that the 2021 fork by someone else has now itself lapsed into inactivity.

saitoha/libsixel looks alive and kicking to me

the x server (OP link) is inactive indeed

	▲	JdeBP 12 hours ago \| parent [-]
		That's interesting. Xe probably should close that issue, then. (-: Also note https://github.com/Kreijstal/libsixel , another fork that sprang up because the author vanished.