I've been using the same Silverblue installation for about two years (maybe even more than that). Initially, I did a lot of tweaking because I didn't really know how to approach toolbox and flatpaks, especially because I don't use Gnome as my desktop environment, so this system went from standard Silverblue to Silverblue+i3 overlayed, then to Silverblue+sway overlayed, recently it got rebased to Sericea and it's still running like day one. It also got upgraded from version 35(-ish) to 38 still without any issues (well, I did have some issues, but I simply rolled back and that fixed it).

I'm also deploying several Fedora CoreOS servers with a similar level of success, but those mainly tend to just run some containers, so I would say I mess way less with those, it's been mostly just update/upgrade to the latest, check if podman is still running my containers and let them be.