Sounds like you actually used the Eclipse Installer, which doesn't use the APT package management system. It just plops Eclipse into a folder on your system, and that's it.
To uninstall Eclipse, you should be able to just delete the following folders. This will delete all installations of Eclipse on your system, so if you're trying to remove just one version, don't do this. OK, here are the things to delete:
~/eclipse/
~/.eclipse/
~/p2/
If you're done with any Eclipse projects, you may also want to delete ~/workspace/
. You may also want to search for any other Eclipse workspaces on your system and delete them, too - search for .metadata
folders on your system, and that should find them.
You might also have other folders you want to delete - for instance, if you used Maven with Eclipse, you may want to get rid of "~/.m2/" (though be careful with this stuff, since some of that data may be shared with other IDEs on your system!)
Final note: This is just an adaption of an answer by kapex on Stack Overflow that has more info. The answer is regarding removing Eclipse from Windows, but the instructions appear to also work on Linux.
eclipse
in Ubuntu 20.04