@chetansha Just today, I've been fighting with Airtel tech support to get them to understand that I want them to enable bridge mode on one of the LAN ports of the Nokia ONT.

Setting LAN port to bridge mode via the ONT web interface does nothing.
Once you put the ONT in bridge mode, did you have to do any additional config on your other router? Did you for example have to set up PPPoE and, if so, how did you get the credentials? Thanks in advance for your help
I am on Airtel in Pune but still on Ethernet, so I have no knowledge of your specific Nokia ONTRouter model. Please share the exact model name of your Nokia ONTRouter for ref.
However just FYR, I have enabled Bridge Mode and set up our own router full-fledged on BSNL FTTH at my relative’s place. Generally, first, you enable Bridge Mode and then do port binding in ONTRouter. This is just a sample screenshot from BSNL’s ONTRouter, your settings/naming/screens, etc may be different.
After that, you need to set up your own router full-fledged (LAN Cable from Bound LAN Port on ONTRouter to WAN port of your own router) including Internet (PPPoE), DHCP, WiFi and everything. If PPPoE credentials are not known, Airtel should provide you the same for your account.
BSNL does not incorporate MAC ID auth nor do they have any dependency on them for Bridge mode. So it was a very simple setup. While Airtel to my knowledge (At least not at my end) does not deploy MAC ID auth, there might be some setting to be enabled from backend (Just a guess). So do check with them if Bridge Mode + Port Binding together does not work.
Generally, when you tell ISP that you want to use your own router, they, on face of it suggest you inferior Access Point Mode. The immediate Airtel Technician who will contact you may not have enough knowledge of Bridge Mode. Generally, when I have any kind of Advanced query beyond ‘No Internet’, I take a funnel approach to eventually cause the technician to admit that they do not know the solution and this is where I then ask them to conference me with their senior back-end technician. This is the way I actually interact detailed tech matters with their technicians (not field engineers). So try this approach and see if you can get to interact with the person who has some knowledge. Also escalate to net at the rate airtel dot com email id if no progress.