I put a downloaded YouTube greenscreen video into PD365, left the greenscreen background, shortened the clip and produced it as H264 MP4 at 1920x1080.
It will open in VLC and Windows Media Player.
I even put the file in two different online video converters and the resulting file still yields the same error message in PD365
(one week old) Dell xps15 #9510, 11th Gen I9, 32gb ram, 1 TB SSD
Charles