Might be controversial as it is usually intended for gaming but: Bazzite (Gnome Edition). It is like Fedora Silverblue but has distrobox and virtualization baked in without fiddling AND… built in Waydroid so you can run Android apps. I am incredibly impressed with it.
He specifically mentions containerization, Flatpaks, Docker and Toolboxes, which these suggested Fedora Spins are designed to integrate with as tightly as possible, so completely relevant.
Also, Bazzite is completely the opposite of an OS designed to run one app at once, which means you haven’t tried it before rubbishing it as a suggestion.
p.s. Don’t take this the wrong way but the phrasing in your comments here make them sound quite aggressive and could lead them to be interpreted in the wrong way. Would you speak to someone like that on the street?