I may be wrong about this being illegal (depending on the country you reside in), but it is certainly not an approach that scales. Meta/Instagram have multiple teams dedicated to preventing this type of scraping. Unless you're willing to invest an equivalent level of resources, any success in scraping Instagram data will be temporary.
> it is certainly not an approach that scales
If there's demand for their service I don't see why it wouldn't scale. Get more phones, more SIM cards, and have automation around all this infrastructure to automate away as much of the stuff as possible.
> Meta/Instagram have multiple teams dedicated to preventing this type of scraping
That's great but ultimately they still have a weakness: they want people to be able to see their stuff - at least some of it - without logging in. As long as you can either simulate a normal device perfectly, or even better, use real devices or virtualize them, there isn't much that Facebook can do without impacting legitimate usage which they don't want.
The only way is for Instagram to restrict registration altogether, but you might create a black market where existing users sell their accounts, and cannabilize its own userbase (Bad for meta stock prices).