GPG error: The following signatures were invalid
Posted: 30 Jun 2021, 20:42pm - Wednesday

W: GPG error: https://dl.yarnpkg.com/debian stable InRelease: The following signatures were invalid: EXPKEYSIG 23E7166788B63E1E Yarn Packaging <yarn@dan.cx>
E: The repository 'https://dl.yarnpkg.com/debian stable InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

Solution:

sudo apt-key adv --keyserver hkps://keyserver.ubuntu.com --refresh-keys