> Is it uncommon to do some free software work in your spare time?

No. But life for many people consists of more things than just software development.

If it's "work work" (tasks you're being employed to do) then it's illegal in most of the EU to work every day — see the Working Time Directive¹, which requires at least 24 hours of non-work time every week, for most occupations.

I'm paid to work on free software. In the last year, my Github profile shows a single commit on a weekend, when I made a pull request on a browser extension I use. I'd rather spend my weekend time away from computers :)

[1] https://en.wikipedia.org/wiki/Working_Time_Directive

"Free time" is when you do it, sure. The point is that you are not a machine and probably should not be working on code every single day.