I went ahead thinking it might add it to the 2021 version, but upon closing and reopening it, it doesn’t seem to have worked. I even checked the customize toolbar menu to see if it was in there. Unless it’s right in front of me and I’m not seeing it?
I was just kidding. There was a recent trial between Epic and Apple. Twinmotion is owned by Epic and MacOS is declaring it not trustworthy. Coincidence.
Did you read the Apple support page? You need to open security preferences and choose to open anyway without certificate, then the installer will open.