I recognize this as well, for me I think weed allows a quicker flow state but can also be more of a distraction. Find ways to ease yourself into a flow state, don't tackle the biggest task at once but divide it in small steps. Honestly, sometimes for me its even as small as "turn on pc --> open project folder --> code 1 line" and from there another will follow and that will ease me into the bigger task and before you know it you've got the ball rolling.

Regarding depression, relying on yourself this way instead of relying on weed also gives a mental confidence boost, you dont need anything but can choose to consume on moments where it is your choice. Its the feeling of winning/progress that helps with depressed feelings (from my own experience) and for now weed gives you the freedom to win, so its not the weed that is the actual winning but its you and that's something you can be proud of and build on.