I’m also not quite sure of how it works yet but at least the first part is correct i think. The full link worked for you because its to the instance your account is on. When i use that link (on the desktop website) i get redirected to that site but i don’t have an account there so i cant interact with it on this account. Similarly: if I link https://lemmy.blahaj.zone/c/antiquememesroadshow@lemmy.world it will work for me without problems but you should see a website where you aren’t logged in (at least using the website, mobile apps might handle it differently i think).
(Although i have no idea why the exclamation mark link didn’t work for you, it did work for me at least. Maybe its the app you are using? I remember that for example some old jerboa version had problems with the exclamation mark links where it would just crash when you tried to use them.)
Thanks for the detailed explanation on the sysreq keys & when & how to use them for unlocking a frozen system :D. Also for the
systemctl
bit because i wasnt even sure what to do if i had gotten to a console lol.