How to change keyboards layouts backwards?

I added a few layouts set a keyboard shortcut to switch forward, but how do I switch backwards? Pressing shift along with the shortcut doesn’t work and I haven’t found a way to set it. The best would be a pop-up menu I can control with the keyboard (like in Windows), but even just being able to go up on the list would help. (I have 11 layouts I switch between.)

There is no “previous layout” setting, just “next layout”, but you could set for each a shortcut, or break down their order in logical groups, in something that makes sense to you, and you switch to one of that logical group, then move next with the main shortcut.

Is there some program I could use without having to install a different desktop environment? It’s just very cumbersome as it is right now.

Not sure what you want to imply

That in itself is cumbersome … There is no better way to deal with it unless you click on the menu and chose the layout, or use mouse-wheel to navigate forward and in reverse/backwards.

At this point you should know better than anyone, since you use so many layouts. The one integrated in KDE Plasma is the best there is. It simply has no previous layout setting. Maybe ask KDE Plasma developers to implement that, in a enhancement UI request.
Or follow some tutorials how to deal with multiple layouts in a optimal way:

Use a custom toolbar:

I’m not very experienced with linux, so I don’t know how if it is possible, but I would like to know if it’s possible to install the keyboard switching function from Gnome on KDE, or if it’s a part of Gnome that you can’t just install on a different desktop environment.

(It’s difficult to explain without being able to post links, so forgive me this mess:
regex to fix it for your convenience:
sorry for the inconvenience)

So I tried Gnome and turns out that has a hard limit of 4 keyboard layouts at a time. KDE seems to have a limit of 8 as well. It seems like a weird restriction, are there some config whiles where this can be changed?