I have quit maintaining 3 big FOSS projects in my life, the first of them I did badly, two I did well. In each case it was because I no longer used the software myself.

The bad case, I just stopped working on it. If you're a user of it, move on the moment you see it stagnates for, say, 6 months, especially nowadays.

The good cases were:

1. Found a really good maintainer so I transferred repo and package ownership to them. This is still alive today.
2. Gave people a much better alternative. Told users to migrate and set a deprecation date 1 year after. Had a little bit fallout but when I archived the repo after a year, there were tons of user reports in public on what to do.