Short answer
Yes, a tiny taste of ripe jackfruit flesh is safe for a kitten. The soft, ripe fruit in a very small piece is fine, but avoid any seeds. Because kittens are small, even safe foods can cause an upset stomach if they eat too much. Offer just a tiny bit, watch for any vomiting or diarrhea, and call your own vet if anything seems off.
Jackfruit — Food safety facts
Safe to share · Cats · full breakdown on the linked food page
Ripe flesh in small pieces is safe. The seeds must be boiled and peeled before they are safe.
The full verdict, portion guidance and serving notes are collected on the Jackfruit food facts page.