Multi Camera Combination with adjusted aspect ratios,Screen made up from RenderedTexture Elements

Hello guys,

I'm new to Unity and I would like to make a smartphone game (portrait mode) which has its view made up from different screen 'modules'. While the overall output resolution will be e.g. the resolution of an iPhoneX, the different screen 'modules' or components will have totally different aspect ratios.

I'm not sure how to do this - so maybe you can guide me into the right direction.

Right now I am trying to use different scenes with different cameras and put the cameras output into a renderedTexture which I will use in my main view. However there are multiple issues with this (maybe because I'm a beginner) ... I cant even match my individual cameras to individual aspect ratios or output resolutions ... all cameras always apply the same (game's) aspect ratio. Coming from 3D Studio Max ... I am used to create a camera in my scene and specify its output resolution ... so I could have many different cameras with varying resolutions. Thanks for your help!

maybe this image helps to understand my question...

[1]: https://i.ibb.co/p40gKw0/description.jpg