It's not a lion's roar for sure and the F-35 was involved. For detail take the word of God from the Hollywood Reporter:
Did you use other archival elements from the animated movie?
There's a moment where Simba roars and we think, "My God, how did he
make that sound?" and we come to discover it's Mufasa. And Jon said,
"In that scene, I think they used some things other than lion vocals
to get that intensity to the roar" and [supervising sound editor Frank
Eulner and I] said, "Okay, we better get those elements." They had
actually used an F-14 (aircraft) as a component and a number of other
things. So, I took that and I thought, "Okay cool, I can use that.
I'll put it in, but let me embellish it and see if we can make it even
cooler." And so I used an F-35 and some other elements, and that
roar became a big climatic moment that borrows from the original track
and also is kind of glorified by other elements as well, some of which
are not lion, and that's the only case where I did that. I was very
careful that we used lion recordings in every other moment of the
Also from MPAA:
Boyes says. “Jon wanted to reference the original film so the Mufasa roar you hear is the same but we included additional elements as it’s meant to be one of the strongest roars in the film.”
There are no specific words about using a tiger's roar but it suggests they did it same as the animated version with some addition.