OS: macOS Big Sur 11.0.1
$ java -version
java version "1.8.0_271"
Java(TM) SE Runtime Environment (build 1.8.0_271-b09)
Java HotSpot(TM) 64-Bit Server VM (build 25.271-b09, mixed mode)
Right clicked on the installer.jar in order to get past macOS security settings, and select Open With JavaLauncher.app
The Mod System Installer window appears, asking for whether to install client or server. I ensure client selected, then click OK
A log window appears and then disappears quickly.
In the directory the installer jar file is located, a log file is generate. Log file attached.
forge-1.16.4-35.1.0-installer.jar.log