Was about to say, I've been using the launcher just fine since July on macOS. At least you got it working now.
As for the launcher thing, that's intentional. You can either use the launcher with non-Jagex accts, and can have multiples added to it, or you use it with a Jagex Account.
With the future being just Jagex Accounts, and this being more of an early adoption system, that's likely not something they're going to change.
You'd have to load the client normally and sign in through the old login portal to access the account that way until JA's become required to use; or, import them to your Jagex Account, and whenever they log into their accounts, just load up the client with the selected one.
Can I turn in a paper without citing all sources?
"No."[1]
1. William Shakespeare,
Hamlet
, Act III, Scene 1, line 96.
04-Apr-2023 16:44:02