Due to changes in the way macOS Catalina 10.15 allows installers to run, there may be some additional steps required to run the Infinity installer:
- Double–click the downloaded Infinity435.dmg file so that its contents open in Finder.
- Control–click the Infinity 4.pkg file to display its menu:

- Click Open, so that the following dialog box is displayed:

- Click Open and the installer should run as normal.