When it comes to big providers like them you can assume that all numbers are either used by other people already or blocked.
If you just don't want to give out your number you could get a second one? Nowadays with eSim it should be easy to get a "pay as you go" number and only ever receive sms.
I eventually did get a second number and was still blocked by Instagram. Perhaps it was because of earlier attempts with temp phone numbers (I didn’t use VPN). But I don’t know for sure. I gave up after that.
