it's because the cache store SPI changed during the 6.0 development cycle and not all stores have been ported.
We have many many stores now, many of which were contributed by the community. Therefore we have decided to move less-used stores to their own dedicated repos on GitHub in hope that users who need them can update them to the latest SPI.
Regarding the BDBJE store, you can also look at some alternatives: we now have have the new SingleFileStore and the LevelDB store which can provide much better performance.
Okay. I had already switched to the new SingleFileStore but saw that there were not updates to bdb je store so was curious what happened. Thanks for the info.