i avoided flatpacks before.
but now that i tried out silverblue and had to rely heavily on them,
i have to admit that flatpacks are not nearly as bad as i thought.

the only issues i encountered are with steam (might not start propperly on first launch)
and with ides(terminal starts inside the sandbox)

other than that it works great.

I accept that I'm in the minority on these things, but I value simplicity really highly, and I mean "simple" as a very specific concept that's different from "easy". It can be harder to resolve library dependencies on a system where everything is installed using the native package manager and common file systems, but nothing is as "simple" as ELF binaries linking to .so files. Nested directories branching off of / is "simpler" than containers.

Do I have any practical reason for preferring things this way? Not really. There are some ancillary benefits that come from the fact that I'm old and I already know how to do more or less anything I need to do on a Unix system, and if you tell me I need to use flatseal or whatever, I'd rather just use users and groups and tools that have been fine for me for 25 years. But that's not really why I like things this way. I have no issue with embracing change when it otherwise appeals to me --I happily try new languages and tools and technology stacks all the time. What it really is is that it appeals to the part of my brain that just wants to have a nice orderly universe that fits into a smaller set of conceptual boxes. I have a conceptual box for how my OS runs software, and filling that box with lots of other smaller little different boxes for flatpack and pyenv and whatever feels worse to me.

If they solved practical problems that I needed help solving, that would be fine. I have no problem adopting something new that improves my life and then complaining about all the ways I wish they'd done it better. But this just isn't really a problem I have ever really needed much help with. I've used many Unix systems and Linux distributions as my full-time daily use systems since about 1998, and I've never really had to spend much effort on dependency resolution. I've never been hacked because I gave some software permissions it wouldn't have had in a sandbox. I don't think those problems aren't real, and if solving them for other people is a positive, then go nuts. I'm just saying that for me, they're not upsides I really want to pay anything for, and the complexity costs are higher than whatever that threshold is for me.

I use Flatpaks for everything I can. I like how Flatpak keeps apps in a container isolated from my system. Also, Flatpaks contains every lib in every version I need for my installed apps, which means It does not rely on my system libs, and I like It, cause my system libs is to make my system works only.

Flatpaks are just the future of packaging

No, because I don't have a very powerful computer

Even if I did, I would still prefer to have native applications because it would be more permissive

This is exactly what flatpaks were meant to do. Simplify the program deployment across all distros

100%. I just wrote a long post surmising this somewhere, but I'm switching my 5 year old Arch install to something like Debian Stable/Testing because I use almost entirely Flatpaks for my user applications (I would do 100% of them if every app I used had a Flatpak), and it's really just a much better idea to run bleeding edge on only the stuff you care about instead of an entire system.

I don't like flatpak or snap or any of them. System libraries exist for good reason, just because your computer is stupid fast and you have enough disk for the library of Congress a couple times over doesn't mean you should run a veritable copy of your whole operating system for each program. IMO it's lazy.

Sandboxing is a different thing though, if that's the purpose then it's doing it right.