"Minimize" icon displayed on already opened applications
Minor bug. Done on Linux Mint 20.3 "Una", XFCE 4.16.
Upon closing an app, and then opening it again, xfwm opens that application in the same position and shape that those of the last occurence (especially when the screen is split in two by snapping the window to a border). But upon opening that same application, the "minimize/maximize" button displays the "minimize" icon instead of the "maximize" button, even if the window does not cover the full screen, although it still maximizes the window when pressed.
This can be reproduced on pretty much any app that can be re-opened with the same shape, like Thunar (on the other hand, apps that always open with the same position and shape like the XFCE terminal don't have that problem).
TL;DR, the "minimize" icon is displayed instead of the "maximize" icon when re-opening an application that had a given shape, but the effect of the button is still what's expected (namely, maximizing the window).