Yes. I don't remember exactly when Direct2D was implemented, but indeed you cannot *easily* get the same transparency with 2018R1 through 2019R1.1.
The only way to get an effect of transparency with latest Xojo Windows canvas, would be to take a screen shot of what is behind the canvas, and draw it on it.
It should be possible, though, to bring back the truly transparent canvas in a plugin. It would just be necessary to create a custom control around a good old Win32 canvas !
The reason why the canvas displays as transparent in the IDE is probably because the IDE does not show you the true control. Or that it still uses the Win32 control ;)