> churn in the address range where a potential hidden volume lies.

You’re assuming separation exists. VeraCrypt specifically and intentionally allocates the hidden partition blocks from the unallocated space within the normal partition. You know, the same thing that would happen if you wrote a file. Even if you had access to the “open” partition, you couldn’t conclude that “there’s allocated blocks but no files, thus hidden partition” - that presumes the filesystem would TRIM immediately, which is indistinguishable from “there’s just a lot of deleted files that haven’t yet been GC’ed”.

Now to be clear, VeraCrypt specifically is believed to be susceptible to SSD side channel attacks, but even still it’s not definitive conclusions. You’re less likely to be betrayed by the firmware than the OS helpfully remembering you opened a file on a hidden partition and saving that history into the unhidden partition.