>> Actually, it's not a new command, but a new function for C-M-<RIGHT>
>> via forward-sexp-function.
>
> It's an interactive function, so it's a command.
>
>> When a ts-mode defines the 'sexp-list' thing, only then it's used.
>> Otherwise the current implementation with 'sexp' is used for C-M-<RIGHT>.
>
> Then why is the new function interactive?

Ah, I didn't notice it's interactive!

treesit-forward-sexp-list was based on treesit-forward-sexp
that has the interactive spec added by Theo in the commit 207901457c01.

I guess that Theo decided to make this function interactive
for such use case that users could use it separately
or bind it to a key.

What really needs to be interactive is the new function
treesit-forward-list added in the following patch
because there is no special variable forward-list-function for
forward-list like there is forward-sexp-function for forward-sexp.
So users might want to use it separately: