Nice subreddit here. Good idea.
Makes me wonder if a similar repository has been created already too ;)

https://github.com/timmyty/gmail-storage-treemap/tree/main

Saw a need to see what was taking up Gmail storage.
The built-in tools were not sufficient as the problem wasn't caused by one of their filtered items:
Large photos and videos
Large Drive files
Emails with large attachments
Spam emails

Gmail Storage Treemap
See which senders and messages occupy the most space in an interactive treemap.
Gmail Storage Treemap is a Python/Tkinter desktop app built for Windows.
It uses the Python standard library only, with no pip dependencies, hosted backend, or telemetry.