Whilst trying to follow the Frames example on your YouTube channel, I am not the TFrame component as specified at 6:44 the 'Standard + Frames' does not appear.
Using Delphi 10.3 CE and Web Core 1.3.3.
Did you try to add the frame via the project manager context menu:
Add new, Other, Frame ?
Problem occurred as I had previously installed 1.2 on Delphi 10.2. After upgrading I did not reinstall 1.2 and installed 1.3 onto Delphi 10.3 with some files about that I was unaware of.
Uninstalling 1.3.3 and reinstalling sorted out the issue and all is well now.