If it's anything like our place guards and drivers are still at a premium owing to shielding, COVID positive cases and track and trace isolations. Part of the rationale for the reduced service is the reduced number of available staff.
There is an agreement in place that if a member of staff isn't allocated a train to work they will be available at home to come in at short notice if required, so it is theoretically possible yes to be paid to do nothing.
Personally I've not had a spare at home shift in a very, very long time. I was pencilled in for one last week and got called up with 36 hours notice to work a diagram.