Just saw this on the Roma Pass website:
http://www.romapass.it/en/buy/
The service with Roma Pass is temporarily suspended with GALLERIA
BORGHESE. We apologize for the inconvenience.
I've no idea what they mean by "temporary" but wouldn't hold my breath. And on the museum's ticketing website (https://www.tosc.it/tickets.html):
Info Roma Pass We hereby inform you that the agreement between Roma
Pass and Galleria Borghese starting from June 15th,2019 is no longer
active For this reason, reservations using Roma Pass are no longer
accepted. Visitors will be asked to pay their tickets following the
price categories provided by the Ministry.
One more strike against the Roma Pass, IMHO.