And yet, open source software lives and dies on support. Projects that are perceived as having unresponsive upstreams that don't support the project are often in a death spiral.

Fair.

I think what they mean by supported though is (in a very simple example) if you complain about a missing button but it's because your DE theme washes it out then they aren't going to help, otherwise they'd look at the issue and try to resolve it. I think this is reasonable. Sure there's no awareness, consideration, capacity and all that but a reasonable attempt at support.

I think "unsupported" here clearly does not mean a legal obligation to support, but rather "support" in the sense that in the free software community, it is convention for developers to provide help to (nonpaying) users, and that convention should not apply if users make certain changes to the software.