Fixing the Cursor (and Other) Apt Repository NO_PUBKEY Error

You install Cursor (or some other .deb), everything seems fine, then the next sudo apt update greets you with: W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://downloads.cursor.com/aptrepo stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 42A1772E62E492D6 W: Failed to fetch https://downloads.cursor.com/aptrepo/dists/stable/InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 42A1772E62E492D6 W: Some index files failed to download. They have been ignored, or old ones used instead. This happens more often than it should with third-party packages. The .deb installer adds the repository entry but doesn't always correctly install or reference the signing key. The result is a repo that apt refuses to trust. Here's how to fix it properly, plus a couple of related annoyances…

Commenting on Bubbles has been removed. Why? If you want to talk about this post, write to the author, use the comments on their blog if it has them, or reply with a "RE:" post on your own blog. Suggestions? feedback@bubbles.town