Does anyone know how to hide this superfluous option box?

My software provider recently issued a new version of a bookings widget, however, there is a redundant options box that some of their users need but we do not.

To locate the offending options box:

1. Press SELECT on *any of the ‘Book an appointment’ accordion options.
2. The offending box is named ‘Any Staff’ on the Select Provider page.
3. I would only like the single, named staff member shown that was pre-selected on the preceding page.
4. Just in case this isn’t obvious, can it be hidden on all accordion options? (I’m guessing the second page is dynamically created?)

https://www.sohovocaltuition.com/test-booking

I have tried my basic CSS to hide it but their new code includes ‘MUI-boxes’, which I am not familiar with.

.MuiBox-root mui-1sbw9j3 {
display: none;
}

Have I messed up the code or target, or do mui-boxes need a little something else?