ːhappy_yetiː FINALLY!
Steam features on MacOS are now fixed, so DLC and achievements are working
You will get all the achievements that you should for current and previous runs. Two exceptions:
You have beaten the final boss, and reset the game after it - this particular achiv won't be recovered. You need to beat him again, sorry ːstimulationː
If you made a total reset, the game can't remember your achivs before this