I think Github is a relatively simple issue. There isn’t really a shortage of european (or just selfhostable) alternatives, and the way git works means that most contributors have complete local copies of the codebase. TBH I worry more about the ability of american contributors to continue working on a project if the code is hosted in europe - basically a lot of open source developer teams could end up being split or shut down entirely. And the bigger projects like Linux and a lot of the intermediate layers between the Linux kernel and applications are majorly backed and developed by american companies and their employees.
A 16:9 screen is basically two squares side by side, so instead of making a big square they can just make the landscape monitor bigger until it’s large enough that you can comfortable view two documents side-by-side. I definitely prefer 16:10 or 3:2, though.