Here is what I found. Run verbose map * and you’ll see:
x * * y/\V<C-R>"<CR>
Nvim builtin
Last set from Lua
Press ENTER or type command to continue
According to the docs (:map-listing), the * before the rhs means that it is not remappable. I’m not entirely sure if this explains why your mapping doesn’t work.
But here is how you can make it work. Use that exact same definition in your mapping: