Fedora Silverblue certainly seems popular here. I use it regularly and it’s been solid. I’m not sure how many people use Silverblue, but I recommend evaluating it!
I have been tempted recently to install Fedora Silverblue for trying it a daily driver in a spare computer I have at home, however, I read in many forums people having to implement some nasty workarounds for common things I use (e.g Docker/Podman). Perhaps in a near future when I have more time.
Technically you can install whatever you want the traditional way by "layering" it on your base image. I.e. just do a `rpm-otree install <package>` instead of `dnf install <package>` then reboot.
The hard/fun part is just figuring out a way to install and use the software you want without doing that, since that kind of defeats the purpose of using silverblue in the first place. In most cases, you can use a flatpak, a toolbox, or a container.
However, if you can't figure it out, there's no real harm in giving up and layering whatever you want.