disclaimer: zero instagram experience

From <1yo results on setting up an anonymous instagram account: Different email address, different phone number and I'll add setting up from a different device and IP.

    Lots of email options, like disroot.org.
    If your phone takes a physical sim, you can buy a new prepaid starter.
        Or sign up with a MVNO like anveo.com and get a forwarding number
        (incoming text only w/ that last)
    A public library would connect you with a different device and IP

If you succeed, there may be some risk of identification when you add family to your contacts. I'm not savvy enough to guide you thru that tho.

ref: https://kagi.com/search?q=How+to+set+up+an+anonymous+instagr...