Do this 1st:
https://support.surfshark.com/hc/en-us/articles/360009643980-How-to-enable-Developer-options-on-an-Android-device#:~:text=Open%20Settings%20on%20your%20Android,to%20tap%20to%20enable%20it.

Then do this:
https://android.gadgethacks.com/how-to/watch-2-videos-simultaneously-your-galaxy-note-20-note-20-ultra-0337652/