Same problem here with the architect installer. Had this already on another machine and fixed it by hand but I guess its a real showstopper for new users.
downloading lib32-nss-3.60-1-x86_64.pkg.tar.zst...
downloading lib32-vulkan-icd-loader-1.2.162-1-x86_64.pkg.tar.zst...
downloading steam-manjaro-1.0.0.68-1-x86_64.pkg.tar.zst...
checking keyring...
checking package integrity...
error: confuse: signature from "Baptiste Jonglez <baptiste@bitsofnetworks.org>" is marginal trust
:: File /var/cache/pacman/pkg/confuse-3.3-2-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
Do you want to delete it? [Y/n] error: failed to commit transaction (invalid or corrupted package)
Errors occurred, no packages were upgraded.
==> ERROR: Failed to install packages to new root
I did a Refresh Pacman Keys before starting the installation.
My ISO file: manjaro-xfce-2020.2.1-210103-linux59.iso
Update:
I was able to fix this by following this guide [FAQ] Issues with “signature is marginal trust” or “invalid or corrupted package” - Newbie - EndeavourOS to reinitialize the GPG keys:
pacman-key --keyserver keyserver.ubuntu.com --init
pacman-key --keyserver keyserver.ubuntu.com --populate archlinux
pacman-key --keyserver keyserver.ubuntu.com --populate manjaro
pacman-key --keyserver keyserver.ubuntu.com --refresh-keys
After this pacman-key --list showed that the key from Baptiste Jonglez went from marginal to trust.