arning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).

The warning you mentioned is related to the use of the `apt-key` command in managing keyring files for package repositories in Debian-based systems. Starting from Ubuntu 20.04 and Debian 10, the `apt-key` command has been deprecated, and it is recommended to manage keyring files in the `trusted.gpg.d` directory instead.

To address this warning, you can follow these steps:

1. Open a terminal.
2. Create a new file in the `trusted.gpg.d` directory:

   sudo touch /etc/apt/trusted.gpg.d/custom.gpg

3. Import the GPG key using the `gpg` command:

   sudo gpg --dearmor --output /etc/apt/trusted.gpg.d/custom.gpg /path/to/keyfile.gpg

Replace `/path/to/keyfile.gpg` with the actual path to the GPG key file you want to import.
4. Update the package lists:

   sudo apt update

By following these steps, you should be able to manage keyring files without triggering the deprecated warning.