UPDATE
got my monitor working. Go to the settings menu and open “displays”. Use “gather windows” button on the screen. This will bring your external monitor settings forward. Change your resolution and refresh rate for your external monitor. After about 5 seconds, my external display came back to life!
CrispyCritterz
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With the new Big Sur update, my iMac’s secondary monitor hooked up through USB-C to HDMI adapter stopped working. I was able to get the monitor on by using mirror screen, but I cannot use as an extended desktop. All beta versions leading to the latest version worked without issue. This should be worked out before final release.