Quick fix that worked for me:
curl -s https://repo.mobian.org/mobian.gpg | sudo tee /etc/apt/trusted.gpg.d/mobian.gpg
Source: Matrix Mobian chat.
edit: to slow
curl -s https://repo.mobian.org/mobian.gpg | sudo tee /etc/apt/trusted.gpg.d/mobian.gpg
Source: Matrix Mobian chat.
edit: to slow
