It's not that they've introduced bugs, so much as their removal of 'from behind' advantage, and locking sneak attack so you can't select it when the game doesn't think it's valid, has allowed the existing bugs with sneak attack to become more visible to the masses.
Mechanically, you should be able to apply your sneak attack as long as you have advantage on the attack roll - and that advantage can come from *any* source.
You can also apply it if there is an enemy of your target (not necessarily your ally, just something that is hostile to it) within 5 feet of it that is not incapacitated (and thus able to harass/threaten it/occupy its attention); you don't need advantage, but you must not have disadvantage in this situation.
In game, however, this doesn't work smoothly and there are many situations where it fails to apply or doesn't work correctly.
The best thing any of us can do for sneak attack at this point is to take save files that illustrate the bugs (I.e. a save in a combat situation when it's your rogue's turn, and you are in a position to have sneak attack apply, while the game does not let you), and submit them to Larian directly in a formal bug repot, using their form. (
https://larian.com/support/baldur-s-gate-3?ver=4.1.1.1203230#modal) (It's best if your report contains the actual save file plus the thumbnail image that will be in the same folder, and not just a screen shot that you take yourself - this allows them to replicate the issue directly)
