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:

1. Double–click the downloaded Infinity435.dmg file so that its contents open in Finder.
2. Control–click the Infinity 4.pkg file to display its menu:

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

4. Click Open and the installer should run as normal.