I installed Manjaro-ARM-plasma-mobile-pinephone-dev-20210315.img.xz, and it didn’t work, so I installed Manjaro-ARM-plasma-mobile-pinephone-20210315.img.xz and THEN switched to the testing branch. Very little was downloaded. So, I take it that the best way to contribute to testing is to install dev-20210311 and THEN switch to testing with the pacman commands above? AND, don’t update kwin and kwayland-server (how do I configure Discover to prevent updating that?).
You’re probably thinking at this point… RTFM. I still need to read " [Wiki] How to contribute to Manjaro ARM" 