I found the answer. You need to book a “Ticketed Entry”, not a “Digital Pass” for Yosemite. Select “Current Pass Holder” under “Guests” on the first page, if applicable. I booked two passes. $2 each, but I have to show my Senior Pass when I enter the park. It’s a day pass, valid from 5:00 AM to 11:00 PM for seven days. It’s not clear what happens if I try to enter for my 27-mile dayhike before 5:00 AM or if I come staggering out after 11:00 PM.