Try any or all of the followings:
Use follow/unfollow/like method with correctly targeted audience;
Use hashtags to appear at the top of hashtag posts, but don't use very saturated hashtags, 20k-200k post amount hashtag range is good imho for your amount of followers (btw also depends on your engagement rate);
Engage with your followers (i.e like/comment their posts but don't overdo it) so you get high engagement rate;
When you will get >10k followers, search for profiles within your range of followers and offer them shoutout for shoutous;
Post high-quality contents.
imho OP, It will take years.......... to reach 1.000.000
Why not buy followers instead?
Or mix between this method and boosting it.
Don't get me wrong, that's great method!
You might be correct, buying followers could help him achieve the goal but honestly, we aren't provided with enough information by OP as to why he needs to grow his account to 1M followers and what's his plan after that, so I can't agree with you on here nor disagree. Fake followers are good if you need followers just for sake of it, but you can't expect high-quality account after using it, also ER will be terrible.