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..."
It's almost like you are thinking of it as an expiration date and the software has spoiled.
Now that I think about it — it is a python wrapper around a boost library and neither of those have made backwards incompatible changes in a long time which is quite suspicious.
Rust and other compiled languages that have backward and forward compatibility in mind do much better.
Just a small anecdote of Boost changing behavior that broke some of my stuff.
Else, ask for a new maintainer. While code can be considered done (especially if no new features are added), it should never go unmaintained. If it's actually used a lot of course.
There might be a maintained fork/separate project that does what I want that I would like to find instead. Or maybe I was just searching to save myself 30 minutes on a one time task and I'm not up for adopting an abandoned project.