i havent yet got the 'priority target' to work in any battle
If i click the target icon or use 'T' and then right or left click an enemy unit, it seems to ignore me.
Yes, of course ignore.
Why would the developers needed to do as the other games (attack + click on the target), but the call this so exotic?
The manual is written how it works.
Select the squad/or vehicle or group (it's a better) to which you want to set prior targets. Press T. Tracing by window - targets that must be set as a priority.
Remember that this order is recommendation, not strong to do.
In our game, almost all orders are working with groups, click on a single unit is useless and it is unclear why it is necessary.