I haven't heard this particular incarnation until recently, but [cue spooky panicked voice] "the Mac and the iPad are merging, just you wait" has been something we've been warned about for a decade and counting. I've argued before that if Apple really planned to lock the Mac down to the same degree they have the iPad, it would have happened with the move to ARM-based CPUs and the macOS 11+ UX. The fact that that
didn't happen strongly suggests that it's not on the roadmap. I stand by that. (I also stand by my contention that increased security making some things more
difficult to do is not being locked down. My concerns about Apple's future directions have to do with services and advertising, but that, as they say, is another post.)
At any rate, never say never, but I would be surprised if Apple releases a version of macOS that runs on iPad hardware, even if it's running in a lab somewhere in Cupertino. I've been half-seriously predicting an entirely new operating system built around Swift and SwiftUI that replaces both iPadOS and macOS down the road, but I don't think that's in the near future -- and stuffing macOS on the iPad in the interim just seems implausible to me.