Listen to yourself. What’s a distrobox? Boxbuddy? I’m already annoyed about someone expecting me to learn about this and I’ve used Linux exclusively for 25 years. I actually did Linux from Scratch and used that for 6 months for actual stuff. Telling a noob who wants to do normal things that work on a normal Linux distros that because of the (recommended by you) immutable distro they have, they need a container which has an actual normal linux distro inside it to run the thing they want to run, they’ll want to run away and probably never speak to you again.
And about flatpak: I had so many bugs that somehow only happen when you get the flatpak. And you can’t install command line tools over flatpak, you can’t install servers or drivers. Regular users (especially windows power user types) are likely to run into these things and curse you for recommending the one distro where you can’t just apt install theclitoolineed
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The “slow down and then quickly fully freeze”, while it could be other things, might be a low RAM situation. Could be some buggy program that is leaking memory. Try running EarlyOOM or systemd-oomd.