Apt-scure(8) Manpage for repository

Hi all, I am having this error with sudo apt update
E: The repository 'OpenFOAM® Download bionic Release' does not have a Release file.
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.

Are you still running Ubuntu-MATE 18.04 LTS (bionic) ???
That version was dropped from support three years ago.

It seems that Open Foam® also dropped support for this version, hence the error.

Best to remove that Open Foam® repository that you added.

Or ,if you still need Open Foam® updates, You might first check which versions of Ubuntu-MATE they are supporting and then:

  1. upgrade to the newest Ubuntu-MATE version they support.
  2. add their repository after install

Oh, btw, if you decide to upgrade, that old repository will be disabled automatically so in that case you don't have to remove the repository because it will be done for you by the upgrader.