My best chances to turn a « default Ubuntu » into a « Budgie Ubuntu »?

2

Off the top of my head here is what I would do.

  1. From a command line install the package budgie-desktop-environment - this will install the budgie customisation from UB without the extra packages found in the meta package ubuntu-budgie-desktop
  2. This should prompt you during the install to select lightdm instead of GDM
  3. Reboot and select “budgie desktop” from the lightdm icon next to your user name
  4. Install budgie welcome: snap install ubuntu-budgie-welcome --classic
  5. Optional: Run “Budgie Themes” from the menu and click the “Pocillo” theme to apply all of the UB defaults - icons, theme, fonts, cursor
  6. Optional: from budgie-welcome - recommendations enable the backports repository. Select software & updates from the menu afterwards and fully update. Reboot.
  7. profit!