When our Buzz arrives in about a month and a half (dealer estimate), it will be used at times to transport my physically impaired parents. (Future lack of storage space for the Odyssey we use now is leading to the trade-in of that and our ID.4 on the Buzz).
My solution to the problem of the van's elevated floor was to purchase a
folding metal stool with a rubber walking surface. We place that in front of the open sliding door and they're able to step up onto the stool and from there into the seat. We help them buckle their seatbelt since it can be hard for them to reach behind themselves to do it.
I am able to get into the van's driver's seat without any trouble. I'm assuming/guessing that the Buzz has a similar ride height from what I've seen in photos and videos, and an upright driving position is more comfortable to me than the step-down needed for a regular car (the ID.4 is perfect for me right now, too).
Once my parents are buckled in, they're comfortable and they like the roominess.
Alas, if your relative is the driver, that isn't as viable a solution because then they can't put the stool away once they're in the seat.