Hey man, if ya played through Forsaken, Black Armory, and into season of the Drifter then it shouldn't be too hard to jump back in with Shadowkeep. You should be pretty used to the general flow of the game having played what you have. Go to the moon, do the story missions, check in with Eris and other NPCs, look for the yellow markers indicating quests/gear rewards, and increase your power level by grinding out gear. Patrols, public events, strikes, etc are all what you already have experienced.
I guess things like weapon sandbox updates can be confusing sure, but that shouldn't be frustrating enough to quit the game over. Not trying to like single you out or anything, and I'd encourage you to stick with the game and again just go into it the same way you did in Forsaken.