As explained in this post, since version 6.0 you can no longer use "1" and "0" as Boolean values, only "true" and "false". Because you're running an old version, 5.3.2, it allows you to use 1 and 0 but when you try to index those as Boolean values to the new cluster, with version 6.8.5, it fails.
To solve this you will either have to reindex inside the old cluster first, replacing 0 -> false and 1 -> true, or use an ingest pipeline to replace those values while you index into the new cluster.
Good luck!