Backstab in BG3-EA (hitting around the rear of a target) is a logic that is incompatible with 5e rules unless you add other homebrew rules around it.
In 5e, there is no facing logic (you defend 360) and any creature can run around a target without any risks (no Opportunity Attack risk for moving around a target if you stay in melee).
So, in BG3-EA, if you want to backstab each round, you can most times without risk. I have seen mobs move a few feet to hit me in the back and then move back in front on the same turn :P LOL. I presume most players do not use it every turn just to save time and it would get crazy boring, unless the character has the Sneak Attack feature.
Anyhow, with easy Flanking (with an ally), remove the Backstab unless the BG3 combat system is adapted fully for it (ie. therefore not saying BG3 must be like 5e).