This year, my girlfriend and I were using Google Sheets to track our expenses and compete to see who could spend less money. We eventually decided it'd be a way better experience if we had a dedicated app for it, so I worked relentlessly to build one and polish it up until I was pretty proud of it. I "released" it to a couple of online communities where I thought people might be interested, and I gained exactly 1 active user who I don't know in real life.
It's all good, though, because my girlfriend and I use it every day, so that's all that matters to me :D
But yeah, it can be difficult to "scratch an itch" if you feel that nothing needs scratching. If that's the case, I wouldn't really worry about it. If you don't need to build anything, then don't spend time building anything. It's nothing to feel bad about.
Perhaps the problem is you're wanting a side-project for the wrong reasons.