the docs says "Near caches store data in the on-heap memory. ", https://ignite.apache.org/docs/2.15.0/configuring-caches/near-cache but I know we can configure a cache being on-heap/off-heap, just not sure if it applies to near cache too.
CacheConfiguration.setOnheapCacheEnabled(false)
No is the short answer. A near cache is always on-heap.
I should also add that setOnHeapCacheEnabled does not configure whether a cache is on- or off-heap. An Ignite cache is always off-heap. An on-heap cache is in addition to the off-heap cache.