Nothing significant has changed with mouseover macros since the introduction of @ as an alias to target=, which I believe happened during BC. Also, to my knowledge there are no options in the base UI that you can enable to facility mouseover casting, it all needs to be done via addons or macros.
Make sure you have Interface > Combat > Auto Self Cast enabled.
You have never been able to mouseover your own 3D character. Similarly, you cannot click on your 3D character to target yourself. The reason behind it is that it would always get in the way when trying to interact with things very near to it.
Those options do not affect macros, only spells pulled out of the spellbook; for macros this functionality needs to be manually coded. The macros I posted above have forced self-cast set to alt+key. If you wish to change it to right click (which I don’t recommend because it’ll mean constantly moving your mouse a significant distance away from your unit frames) replace [mod:alt,@player] with [btn:2,@player]