Not shure if I can explain myself propery as I just started the game and am only on the 3rd combat scene I think (don't know much about the game).
Whenever I use energy skills that increase defence I get stuck without being able to do anything.
I can focus on other units but not select them
I cannot select my crad deck
I don't see how to end my turn even if I wanted to (can't left click or right click on the active character)
When the turn timer runs out, nothing happens

I also tried reloading and using defence buffing abilities with another character but I get the same thing.

This sounds like you're using a skill that doesn't end the turn. So you have to click on end turn for the character you used. This can be confusing, because you can only move/use 1 character at a time, but despite that the game will let you select other characters after you have moved but not finished your turn. Only in this case you can only preview the other characters abilities.