The latest Firestick 4K Max is slow, full of ads, and locked down to where some of the more fun side-loading features don't work anymore like remote button remapping. I ditched it and got an Apple TV that doesn't force you to watch ads for Ford pickup trucks.
But Kodi is available for the fire stick while you have to jump some hoops with third party signing services to keep it on Apple TV.
It’s certainly better in other ways but this thread doesn’t follow
Kodi is the only application I run on my Firesticks
I use it to run the Jellyfin client, but it's still painful to use because you can't bypass the Firestick home screen, which is bloated with ads and takes seconds to load. I find this unacceptable in a commercial product.