For example, how do you setup the maximum amount of storage used for trash, like 100GB?

I use Krusader from a docker container in Unraid.

Hi, Krusader is using the KDE trash but doesn't have trash settings on it's own.

These settings can be adjusted in Dolphin or with the "Trashcan" Plasma widget.
They can also be found with the ALT+F2 search with search term "trash" but somehow they are not included in the KDE System Settings UI.