First of all: thank you, thank you, thank you to the Manjaro ARM developers! It's much more like a "real" desktop OS than Raspbian, and my RPi4 comes very close to being usable as a daily driver for my basic needs: music, movies, email, web-based office stuff.
One question on graphics performance: in Manjaro I only get 2-4 fps when running the Aquarium test on www.webglsamples.org - roughly the same performance in Firefox and in Chromium. Running the same test on Raspbian with Chromium I get 26-28 fps.
Movies and streaming content play fairly well on Manjaro, but with slightly more frequent screen-tearing than on Raspbian. It's not a big deal, but if there's a setting I can tweak to fix this I'll do it. Or if it's a coding issue, I'll just patiently wait until it's fixed. (I'm not a coder, but happy to help with testing if that's of any use..)