Can't see `python plugin manager` option on Ubuntu

Where should I look for? I want to install a python plugin.

The Plugin Manager should be the last option in the left column, just under “Color Selector Settings”. How did you install Krita? If this isn’t the appimage from the Krita website, can you try that?

I’ve installed it through the Ubuntu software centre

Yeah, I thought as much. Download the appimage from krita.org instead and uninstall the Ubuntu version.

The Maintainer probably compiled Krita without Python support. The Ubuntu package isn’t maintained by the Krita team.