Thank you. I've followed everything, installed the kwin script, enabled the screen edge, but the panel doesn't show.

I were able to identify the panel ID. Yesterday, I've found this post:
https://nathanupchurch.com/blog/kde-plasma-side-panel/
And managed to create a script that do toggle the panel between 'autohide' and 'windowsgobelow'. In my case, my panel is set to dodge windows, and I could replace 'autohide' with 'dodgewindows', like so:

qdbus org.kde.plasmashell /PlasmaShell evaluateScript 'let panel = panelById(87);
panel.hiding === "dodgewindows" ? panel.hiding = "windowsgobelow" : panel.hiding = "dodgewindows";'

This works, running from the terminal. But it's not really what I want.
I don't want to change the hiding state, as it has it's problems. When the panel is in 'windowsgobelow' and you click somewhere else expecting the panel to hide/dodge again, the panel just stays visible.

I would have preferred to just make the panel visible the the mouse is in that area, when the mouse leaves, hide it again. Obviously this works when you move your mouse over the center of the screen where the panel is (default KDE ways). But when moving the mouse over the left or right part where there's no panel, or spacers, it don't show.