For Windows, WizTree because it’s extremely fast. For Linux, I like ncdu

Just the standard Disk Usage Analyzer that ships with my distro. The visualisations are nice and the nesting of dirs is very clear.

K4DirStat

If I’ve understood the question as you intended it, on windows I use treesize, on Linux I use NCDU

I use the configuration app on Windows 10

Space sniffer. Visual size representation, and easy to jump into directories.

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Also interested.