Your additional ideas that were scrapped sound also very interesting. Maybe you can use them in an update or another game. I can assure you that the flickering is not because of you messing up. It's Unity which messes up your tilemaps :D If the suggested solution in the video does not work for you, there are other solutions, too (e.g. setting the "Pixels per Unity" of your tilemap sprites to 1 pixel less than you have right now).
I get it that you wanted to do another solo project before working with others. I also normally work on my own, but I did 2 projects with my friend now.
For how long have you been in game development now?