Error when building: "Runtime Error: discourse does not support compiling scss/sass files via sprockets"

To anyone encountering this (also note to my future self):

Wait for build to complete and run localhost:4200 instead of localhost:3000 :grimacing: :sparkles:

Build successful message:

Build successful (45326ms) – Serving on http://localhost:4200/

Slowest Nodes (totalTime >= 5%) | Total (avg)
-+-
@embroider/webpack (1) | 22005ms
Babel: discourse-plugins (21) | 8820ms (420 ms)
Funnel (552) | 3371ms (6 ms)
@embroider/compat/app (1) | 2564ms