It sounds like you are doing something wrong when you design your UI. Supporting only portrait, or only landscape, is not a bad thing, but supporting both is better. If you decide that your game will only support portrait mode, that's fine.
However, in the case you want to support multiple resolutions, portrait/landscape, wide screens or CRT boxes, here are some tips:
- UI elements can have a "variable" size that depends on the screen, using anchors. You can for example specify a button that its width is half of the screen's width. This means that regardless if you play on portrait or landscape, your button will resize itself to half the screen's width. This is one way to make buttons be more interactive, but it's not ideal for all cases.
- Using the above tip, you can also tick "keep aspect ratio" on images, so that they resize to the specified width/height, but the displayed image keeps it's aspect ratio. This is more likely to be used on image buttons.
- When positioning elements on the screen, do not use absolute pixels because it works on your editor. Instead, use screen portions. You want a button to animate itself and move to the middle of the screen? Then move it to
0.5, 0.5 if using anchors).
- Another idea which I've used on an android project in the past, is to make a different layout of your UI for portrait and landscape. Simply make a check if
Screen.width is bigger than
Screen.height. Having different layouts makes your game look more professional.
I hope this helps you move to the right direction. For more information, you can read Unity's tutorials: Designing UI for Multiple Resolutions and Basic Layout.