This test is easy to replicate.

I booted into a live 22.04 session and updated the repository (not the packages) and checked the used disk space from the root (alt+enter in nautilus): 362.6 MB (224,147 files). Then I installed dolphin and that's the total amount of space taken: 832.8 MB (235,832 files). Then I removed dolphin (sudo apt autoremove --purge dolphin): 480.8 MB used (226,826 files). According to apt, all the 287 packages that were installed previously were successfully removed.

The second issue happened as the sequence of the commands above. I installed thunar and then removed it: 486.7 MB total used (226,955 files). In this case apt decided to keep tumbler packages even after removing thunar, so 18 packages were installed but only 15 were removed.

Finally, following the sequence of the commands above I installed/removed thunar again, and more disk space was taken as the result. I did the same thing one more time, and surprisingly even more disk space was taken. In the end I had 489.2 MB used with both dolphin and thunar removed, compared to 362.6 MB used in the beginning of the tests.

Hi,

there is nothing surprising about what you observed. I suspect you want to remove the downloaded package files.
Evo2.

don't forget apps usually create some config files or other things which do not belong to the package, but required for the app (like database or just setup/configuration or anything similar). When you want to clean these files too you might need to use apt purge package or even you need to remove those additional files manually (obviously it depends on the app itself).

@evo2, using the command you suggested dropped the used space to 404.4 MB, which is still more than the initial 362.6 MB.

Also, I still don't understand why tumbler was not removed.