Apple really doesn't tell power-users about a lot of these features. You can really gain a lot by searching for Mac shortcuts and tricks. I still learn new things that have been around for over a decade.
⌥k = ˚ (degree) ⌥e a = á
⌥p = π (pi) ⌥e e = é
⌥5 = ∞ (infinity) ⌥e i = í
⌥d = ∂ (delta) ⌥e o = ó
⌥8 = • (bullet) ⌥e u = ú
⇧⌥9 = · (middot) ⌥n n = ñ
⇧ = shift; ⌥ = option[1]: https://support.apple.com/guide/mac-help/use-the-keyboard-vi...
correction: on your macOS menu bar (at the top-right of the screen along with WiFi, time/date, etc)
For completion, system shortcuts are also available in `System Settings > Keyboard > Keyboard Shortcuts...` (where they can also be changed). (Although I don't think that's 100% comprehensive, e.g., I don't think `⌘⇥` for the application switcher is listed there.)