The video the other user posted does help, but I want to add something. There is a mission called "Coming Home" that is part of the 404 chapter, and it's the 3rd mission of the set. This mission is where I got the achievement, as it has a lot of one part collectibles which makes it much easier to gain achievement progress.
Also as you're doing missions, look for boxes in the mission areas. A lot of them can be obtained via spider drone in the areas the main story missions are, so if you look for them as you play, it will save you a lot of time collecting them after you beat the story. Flying on a cargo drone also helps a lot for anything high up, bring a construction worker so you can summon it wherever you need.
Credit to Norm D Minotaur for providing this map from Ubisoft:
https://www.ubisoft.com/en-gb/game/watch-dogs/legion/news-up...