WinDirStat on Windows, I am not at Windows machine right now but IIRC the original WinDirStat walks the whole filesystem, can take long time; faster forks of it use the NTFS Master File Table (MFT), which more like just looking up into already collected by the system.

https://www.idealsoftware.com/opensource/fast-windirstat.htm...

On the Mac, I've used Omni Disk Sweeper for pro a the last 20 years, and it still receives updates. Not open source, but no $$.

https://www.omnigroup.com/more/

(I used OmniWeb as my favorite web browser for NeXTStep, followed it to macOS. Also their pro diagramming tool, OmniGraffle - remember Visio before Microsoft bought it?)