I learned I pretty much never need old data for my hobby selfhosting stuff. So I do 4 weeks. I'll notice if something breaks within 4 weeks and fix it. I occasionally do manual backups, for example when migrating stuff and keep them for longer. And I got some old stuff like in xkcd 1360.

I suppose I could do more, but I also want the privacy policy of my online services to say: x weeks and all the logs and unnecessary data is gone.