So I've been trying to install Forge for 1.16.3 for the past 3 days and have been running in to this issue. I've tried everything I could think of, even completely deleting everything, my worlds, everything and installing new minecraft installation. Forge will just absolutely not work after using the installer.
I have put the minecraft log file in this post, I'm not sure if that's the log files you guys look for, it's just the only one I know the location of. This has been driving me insane.
2020-11-29-1.log.gz