I have created quick launch app widgets (KDE plasma 5.25 desktop). Is it possible to backup the widget settings so that the next time I re-install plasma I can restore the widgets? Where are the widget related settings stored? Also where are the other settings like keyboard layout or shortcuts stored?

That feature isn't officially available (yet?), but you can use a neat third-party tool named 'Konsave' to do the trick. Check it here:https://github.com/Prayag2/konsave