Chureito Pagoda using a wheelchair?

Is it possible to get to the Chureito Pagoda using a wheelchair so we can can have our picture taken with MT Fuji in the background?

No. There is a long flight of stairs

There is a very long and steep winding road up to the base of the pagoda. You won't get good angles for photos though. And I wouldn't recommend push a wheel chair up. Need to go up in a vehicle.

There is a slope on the side, so you can go by wheelchair, but the road is closed to vehicles. (It takes about 15 minutes to walk from the main hall of the shrine.)
You can go to Chureito Pagoda, but it seems that you cannot go to the observation deck above it because it is a staircase.
https://chureito-pagoda.com/information/blog_2459/

The slope path is also not as steep as the stairs, but it is considerably slanted.
When I operate my mother's wheelchair, I put myself on the lower side (operating while facing backward) on a downhill slope to prevent my mother from falling out of the wheelchair.
In that case, it is likely to use a lot of force on the hand brake.
If you are going with several people, I think it is better to operate by turns.
Alternatively, you might consider securing a person in a wheelchair with a belt.

When I checked again, it seems that you can go to Chureito Pagoda by car from early April.
https://www.city.fujiyoshida.yamanashi.jp/info/151
However, you must call the shrine in advance.
However, please note that it is not allowed during busy periods (cherry blossom season, consecutive holidays, autumn leaves season, etc.) or during rush hours.
By the way, when I went there in February, a car from the tourist information center was parked near the main shrine, and I was able to ask questions. (I spoke Japanese, but I can probably speak English, too.)
But I think you need to make a reservation before arriving at the shrine, so please go there after consulting at the tourist information center.
https://tic.jnto.go.jp/eng/detail.php?id=1113

The stairs up to it are brutal - there is a winding road, but you'd still need someone with a lot of stamina to push a wheelchaired person to the temple. And as said, access to the pagoda is only by stairs.

or shrine, rather. You can look on google maps to see how the road winds to the stop. To me, if the weather is cloudy, no real need to even go.