I contact the local Airtel techlead in my city, he told me there was an update about this in May or June. Some popular tech YouTuber post about it how you can get 1Gbps in 40Mbps plan. All of the sudden, there was huge requests for static IP. So, they have been instructed to deny any static IP request to the personal connection at that time. But now a few days ago, they updated some Noida static IP gateway to force the speed limit. Fair data policy (3333 GB per month) is also implemented for static IP as well. So, this update will roll out to all gateways soon (at least in North India).
I also enjoyed 1Gbps almost for 1year 🫡