I've cleaned my Debian installation as much as possible. I've removed the task-gnome-desktop along with everything I don't want, just whatever the core system + gnome-core and a few utilities. All of my regularly used stuff is now via Flatpak. Gotta move sometime. I like the idea that I get the newest versions + the stability of the Debian base underneath.

Nothing wrong with that. Flatpak, AppImage, containers all get a gig here. With CPU & RAM where they are these days, there is no noticeable impact on performance. Just drop them in and they run. Too easy.

I still don't like it on principle. It feels Windowsy somehow.

I'd add that the reasons for it looking and feeling Windowsy are many.

First, there is the bloated size due to all the static linking thus hogging space on the SSD or HD. Another is vastly increased RAM usage, something which also slows down startup for each program in addition to hogging RAM. Third, their sandboxing doesn't really work in practice like it is theoretically claimed to work, doing an end-run around security instead especially in light of permission exceptions during installation. Fourth, but perhaps first in importance, is that it is much more complex that APT, and complexity is anathema to security and ease of maintenance. Fifth, it does not allow for dependencies brought in from the system's own packaging. On top of all that, it also looks and feels like a trojan for proprietary software and drivers. At least that is what it appears to be designed around. I'll stop there, for now.

I reckon whether it is suitable for anything on my part is whether its goals match mine, and I though I have not seen the written goals for Flatpak I can take a guess.

No thanks. Hard pass.

I use AppImage for the stuff that doesn't come in my distro and would be a pain to build. Right now I'm using Librewolf as an AppImage. If I build it, and something changes in the OS after an update, it might break. AppImage is convenient, but it comes at the price of being wasteful. If I leave this browser open, and start a project under Inkscape (also AppImage), I'll hit the memory limit of the machine since there's other stuff running as well.

So so far I've had to switch both Firefox and Thunderbird back to repo based.

Firefox had some strange stuff about certain things not working, couldn't add a file to Google drive. Couldn't right click and save images, random stuff. Repo works just fine. Thunderbird I changed because it was a bit of a problem adding my gpg key.

Such is life

I've ordered a Steam Deck, and on that, you're supposed to install everything via Flatpak. We'll see how that goes.

A gaming device that they want you to install things via a way that takes more space? That's a very poor stance to push for that. It's already too small an SSD for more than a few games, and if you install anything then they want you to install versions that take up even MORE space so you get to install even FEWER games.

One major difference between Flatpaks, Appimages etc., at least initially, between Windowsy stuff and Linux is as Linus Torvalds sadly pointed out, they are a kind of "necessary evil" caused by some major differences in distros not the least of which is systemd and distro-unique package managers. Windows is basically monolithic while Linux is vastly more diverse. So far with the few I've tried, Appimage has been OK but I've had problems with Flatpak apps even on mainstream distros like OpenSuse. Even though my Main, Slackware, has Flatpak installer available on Slackbuilds.org, for example OBS Studio has no flatpak for Slackware. It does for OpenSuse which is why I tried it there and although it installed, it doesn't run, sort of defeating the design goals right from the jump, no?. OTOH the Appimage for Balena-Etcher, an excellent USB "image burner" app, runs without a hitch and is far better than anything similar even those I've built from source.

It seems to me there are workarounds for size on almost all devices, so I don't care about that if that cost improves my benefits of functionality.... as long as they don't become the exact opposite of what they were designed to do and become yet another force to unify Linux by eliminating diversity and choice.

Frankly I miss the easy days of "Checkinstall" that built distro-specific packages from source.

GCC is the least stable platform I know of. It breaks backwards compatibility constantly.

I've not used flatpack, but do use Appimage. FreeCad and Inkscape now come this way. Works fine on my systems. Not enough disk space isn't an excuse as terabytes of disk space is relatively cheap any more. Memory too. All my desktops/laptops have at least 16GB (my minimum). My workstation has 64GB. So memory isn't an issue either. Should flatpacks/appimages/snap/etc. be used for 'everything'? No. But for big complex projects I can see where it could be very nice as you include known working dependencies with your project.