It is discovered that the Youtube icon was disappeared from my using Dmanager, yet I cannot make any video downloading via Youtube through the Dma

Thank you for your sharing, I had once directly contacted to Apple Support, as what you have said, they asked me to get assistance from the Apps developer.

Then how I get contacted with them for support?

I have tried the primary solution on (1) power off my phone and, (2) Removed the existing ‘Dmanager’ and rebuilt it again, but still cannot help.