I don't know posthog, but I can share some experience with PyCharm and celery.

You need to run the celery worker directly from PyCharm. The detour with watchmedo is not debuggable. For debugging the worker I also need to run it in a local poetry env. Debugging it in a remote Docker interpreter did not work for me either. While the debugger then works fine, it does not reload on code changes any more, which is quite frustrating.

So I usually develop with celery and watchmedo in a Docker container. Only every now and then when I really need the debugger, I start it locally.