This is the first time I’ve heard of this, and I pretty much always have more than one DE installed and have never run into issues. Assuming you’re using a display manager (SDDM, LightDM, etc.), it should handle loading whichever graphical session at the time of login properly.

edit: For clarity, what do you mean by “installing another DE *on top * of an existing one”–like kludging two DEs together in the same X/Wayland session? If so, that sounds like a horrible mistake that lead to that happening.

Same here with the Super+<number> to switch (or equivalent function key if you use that binding for something else), and similarly Super+Shift+<same key used to switch to workspace> to send the current window to that respective workspace. For me, without the second one workspaces are waayy less productive.

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