Doesn't ISS generate oxygen from water and water is essentially shipped in? Either as water or as food. In the end methane is vented to space. I wouldn't call system needing pretty major inputs a self-sufficient one.

You are correct:

>4. Sabatier reactor

>Inside this machine, a blast of roughly 750°F heat breaks the bonds inside CO₂, forcing it into its constituent elements. The carbon and oxygen combine with hydrogen from the station’s ­oxygen ­generating system to make H₂O and methane (CH₄), the latter of which vents into space.

https://www.popsci.com/how-iss-recycles-air-and-water/

Every last molecule used on ISS is boosted from Earth, and recently. ISS does a bit of recycling to reduce the amount needed. There are exactly zero permanent inhabitants: any would die. They exploit no in-situ resource, except sunshine using frequently-replaced solar panels.