The 2021.3 app for EpocCam was released in August of 2021.
This version of the iOS app requires a new driver for Mac or Windows for it to function.
You can get the latest 3.3 driver for Windows here:
How To Solve Flickering Video Problems
If you were using EpocCam in the past, you may have an older driver on your Windows PC, created when EpocCam was being developed by Kinoni.
Using the Kinoni drivers with the newer Elgato EpocCam app can cause problems, including flickering.
To solve this problem, you can fully remove the Kinoni version of the drivers, which are not in use any more.
1) Click on the Windows Start button
2) Write "Apps & features" and press Enter
3) Search for KinoniDrivers
4) Click Uninstall
5) Reboot your Windows PC and then retest it.