IG collects the big data about accs and can join suspicious accs together and match them. And there are many little details:
1) how acc was created: where, which device, phone number, etc
2) how acc was set up: how many photos, bio, options, etc
- By these first 2 IG can joining accs in a groups by the same kinda fingerprints: locations, devices, phone numbers, etc
3) how acc is being logged in: where, which device, security options such as 2fa, etc
4) what acc is doing after: content upload, photos, bio, changing username/full name, etc
5) what is the acc's activity: how many actions, how regularly it performs these actions, is it above the average in terms of activity
6) how it creates the content
And many more little details - by these IG also creates patterns and kinda fingerprints.
So for example if you:
1) buy a bunch of accs that were created a week ago with almost the same conditions
2) then log them in from different IP address locations with obviously VPN/Proxy
3) then upload a bunch of photos and start following people like crazy and start sending them messages
➡️ That all leads to "probably bot" decision from Instagram.
1) Create accs on your own, so you really control the process.
2) Do not log in from another device
3) Do not change the IP address or at least stay within the same City, Country, Region (Europe/Asia/North America, etc) - do not "travel" too far, and if you "travel", give it a time.
4) Do not perform many actions, increase slowly
5) Post some content, watch home page, act like a real human ⚠️