Social media is, in general, terrible. It's full of people and people are terrible. Sometimes strangers, sometimes people you know and (although we don't like to admit this) sometimes the terrible person is ourselves. Dealing with this is not something social media companies are very good at1 but generally at least you have a block function. This has led to some contention about when it's ok as a private citizen to block someone.
YubiKeys are hardware security keys that you can adopt to be the second factor for authenticating to a wide variety of services. They can also securely store keys such that they can't1 be recovered from the device which means they can't be stolen by bad actors.
There are a number of guides out there for doing this many of which are much better written than this blog post2. However they generally tend towards a much more extreme level of setup than I want or need to start with.
With the release of macOS Catalina Apple have decided to finally do something about the very out of date version of Bash they ship. By changing the default to zsh which is one way to deal with licencing issues I suppose. Users of the excellent Homebrew could already install a current version of Bash. But there are more shells in heaven and earth, Horatio, than are dreamt of in your philosophy1.