Error: "Surrealistic-MG-1-Plus-Installer-macOS.pkg can't be installed because its digital signature is invalid."
This problem has been fixed in the latest update for the Surrealistic MG-1 Plus.
Software compiled with Apple's latest OS (Big Sur) produces this error on Macs with OS versions older than 10.12. We'll get this issue fixed as soon as we can. Thanks for your patience!