Biometrics are not discussed much these days because Aadhaar is no longer a strictly biometric id – either at enrollment or in usage.
Biometrics are not collected for toddlers and not considered reliable for under-15s, and that segment was about 30% of the population in the 2011 census. An unknown number have never updated Aadhaar to add biometrics.
Biometric auth fell into disuse with the shift to mobile internet. The government tried strong-arming Apple and Google into taking fingerprint scanners out of the hardware secure zone so they could send scanned fingerprints (minutiae) to UIDAI servers. That didn't work, so they tried coaxing OEMs to make Aadhaar phones with a second fingerprint reader. TRAI – whose chairman 2016-2020 was the ex-UIDAI head – even tried framing it as "device neutrality" borrowing from European app store regulation. None of that worked, so they just moved from biometrics to SMS OTPs for rich people, while continuing to harass poor people for it.
Aadhaar as a unique id was always a galaxy-brained idea when there's no biometrics for children, no removal of dead people, and confusion of uniqueness in an identity scheme vs uniqueness in a much smaller welfare scheme where there's always surplus population who will never notice identity theft.
The only good thing about Aadhaar is the card – it's given people a document that's near-universally accepted. But the Aadhaar card is an organic development that was not part of the original design – where the card was merely meant to be a receipt delivered via the post as a probe to confirm the address – and remains an afterthought in the narrative. Even today you'll find Aadhaar proponents who don't understand how the card is a very different thing from the digital id they associate Aadhaar with.