I tend to check the age difference between the earliest and latest commits because that lets me be sure it's not a project that someone spent a couple weeks coding up, dropped on github, and then forgot about. I'll also check the issues on there. I'm looking for more closed issues than open ones, but I'll also quickly scan over them to get a rough idea of how many are truly meaningful issues. I also get signals from the readme and docs. It's not a hard pass if there's issues with those, but it's certainly helpful to my opinion if they exist and are both clear and detailed.
I really wish GitHub would have some sort of flag for "stale" projects. I use your methods too (issues, dates, etc.), and I'm usually disappointed when search results bring up ghost projects. However, in a few instances, I found a project that was similar to an issue I was working on that went one step beyond where I was, and even though it was a ghost project, it helped. But in general, these projects don't help. I'm also disappointed that I'm thinking, "Hmmm, maybe LLMs can help..."