New insight with a one click fix for errors like this with a server installed 05-2025:

Err:9 https://dlm.mariadb.com/repo/maxscale/latest/apt noble InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5D87FACA8C27D14E

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://dlm.mariadb.com/repo/maxscale/latest/apt noble InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5D87FACA8C27D14E
W: Failed to fetch https://dlm.mariadb.com/repo/maxscale/latest/apt/dists/noble/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5D87FACA8C27D14E
W: Some index files failed to download. They have been ignored, or old ones used instead.

MariaDB changed something last month and would be nice if this can be fixed with an insight.

If the command apt update && apt upgrade returns any error display this as an insight.