Hi I recently installed Manjaro KDE on my 2014 macbook pro (I’m not new with linux) and solved every problem that I encountered at the moment excluding the scroll speed with touchpad (and consequently mouse).
Scrolling webpages or OS menu are a little bit frustrating and I have not found any settings related to scroll speed.
If you are using firefox as browser maybe this link could be helpful:
https://wiki.archlinux.org/title/Firefox/Tweaks#Mouse_and_keyboard
Thank you browsing is a lot better now. I keep looking for something that works in Manjaro menu