If you’re one of those unfortunate souls that run into the following error when running
Err:5 https://dl.yarnpkg.com/debian stable InRelease
The following signatures couldn't be verified because the public key
is not available: NO_PUBKEY 4F77679369475BAA
you are not alone. Fortunately the fix is easy, but it’s buried in the comments, so here it is without a lot of wading:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 4F77679369475BAA
apt update (or the
apt-get equivalent), and you should be golden.