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

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

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

K4DirStat

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

I use the configuration app on Windows 10

Also interested.