I highly recommend checking out either Fedora KDE Spin or Fedora Kinoite! Both are great choices, especially if you want to leverage the power of Flatpak for app installation, as they both push the user towards it. Additionally, if you ever need to install .deb packages, you can easily do so using Ubuntu in toolbox.
Alternatively, EndeavourOS might also be a good fit for you, providing a user-friendly Arch installation with a rolling release system. You’ll have a modern and flexible environment while still being able to use Flatpak effortlessly. You can also install distrobox there to, again, use apt inside of an Ubuntu system.
Whichever you choose, you can’t go wrong! Happy tinkering and remember that the best way to choose a distro is to try it out.
I have a dedicated directory with subdirectories for each project and that’s it