how to convert macOS installer .app to bootable DMG then ISO? A bootable macOS without USB?

​macOS installer.app have to be converted to .iso image to be used in Virtual machines (such as Virtualbox, VMware, ...)

When you download any macOS installer, it comes in the form of installer .app you can follow the steps described in this tutorial to convert installer .app to .DMG then .ISO
1) Using disk utility as described in this video. 
2) Using terminal commands.
3) Using third party application.

just follow the steps described carefully: -

1) Convert .app to .dmg then .iso using Disk Utility:-

- Please watch the upper ☝︎ video carefully and follow the steps. (in case the video doesn't work, press on this link) 
- If you find the video helpful, please press the red button and subscribe to my YouTube Channel where you will find more tutorials. this will be great and push me to do the best :).

​2) Convert .app to .dmg then .iso using terminal commands and parallels desktop app:-

- Please watch the upper ☝︎ video carefully and follow the steps. (in case the video doesn't work, press on this link) 
- If you find the video helpful, please press the red button and subscribe to my YouTube Channel where you will find more tutorials. this will be great and push me to do the best :).

these are the terminal commands used in the upper video: -
a] hdiutil create -o ………… -size 15000m -layout SPUD -fs JHFS+
,b] hdiutil attach ………… -noverify -nobrowse -mountpoint /Volumes/installer_goes_here
c] asr restore -source ………………. -target /Volumes/installer_goes_here -noprompt -noverify -erase
d] hdiutil detach ………….
​e] hdiutil convert …….. -format UDTO -o ……..