Python plugin provides inferior highlighting comapred to LSP supplied highlighting, but it overrides the LSP, so you have to disable pyhton plugin to get better python support.
Python plugin installs pyls, which is abandoned. Currently maintained LSP is pylsp.
Furthermore, pyls and pylsp take extremely long amounts of time to do anything. Autocompletion takes 5+ seconds on my ryzen. This seems to be a longstanding issue, see related issue. Whenever i try to autocomplete or goto pylsp runs at 100% while jedi is at 0% cpu utilization, so i'd guess there's some sort of issue with LSP on qtcreator side, pylsp apparently works properly in other ides.
-slowness can be cured by setting LSP to open per project, contrary to this - https://doc.qt.io/qtcreator/creator-language-servers.html