More common in 1.17 than before, particularly in Shattered Savanna biome terrain.
I was under the impression that all the changes to terrain, including higher mountains, have been pushed back to 1.18 and 1.17 simply added all the "decorative" features; the Wiki seems to agree with no mention of changes in 1.17, only as upcoming features:
Also, people have found even higher mountains in versions as early as 1.7, the last time any changes to terrain actually happened; if the biome is "Savanna Plateau M" or "Shattered Savanna" than it is pretty normal for this biome, but it would definitely be unusual if it were Extreme Hills" / "Mountains":
This is a description of Savanna (Plateau) M from 2013:
Variant of the Savanna biome. Dirt paths and giant mountains are prevalent in this biome. However, this biome is unique in that its mountains can generate past the clouds, and even to the world height limit, without using the AMPLIFIED world type.