I've heard people mention this, but as someone born in Karachi who moved to US as a toddler, I can confidently say I've only ever seen Muslim caste systems mentioned on places like Reddit and HN discussions about caste. It's never come up in visits to Pakistan or when hanging out with Pakistani friends in CA, TX, NJ, NY, or WA.

That's not to say this interfaith caste constructs don't exist, but I've never heard an in-person mention of them in all my life. I'm genuinely curious how widespread they actually are. Were they something that had more weight back in the 16th century, maybe? Conversely, I have heard Indian friends discuss caste discrimination in places like Microsoft.