Went to the mechanic because of noise at speed.
Noise came from rear diff, and they saw metal shavings in diff fluid.
They assume diff bearing has gone bad.

They say the car requires a new rear diff.

How is this possible?
It's a 2019 range rover autobiography with only 53k KM. 5.0l supercharged
Have any of you heard of a diff being replaced after only 50k kms?
Any recommendations on a solution?

No warranty...
Thanks,

I had my rear diff replaced under warranty at 42,000 miles. It was noisy and had debris in the oil similar to you. Never been off road/wading/towing etc so no adverse conditions use. I assume there have been some manufacturing failures with some diffs.

The annoying thing for me was that it sat in the JLR dealership for 3 months waiting for parts.

How about using an Indy to fit a good used unit (one from a salvage car that was in a front end collision maybe?) or have your unit rebuilt by a gearbox refurb company?