SmartTube is an Android app that can be side loaded on an Amazon Fire TV. Developer mode will need to be enabled to install the app.
https://smartyoutubetv.github.io/
https://streamersworld.com/remove-youtube-ads-from-firestick/
https://www.firesticktricks.com/developer-options-firestick.html
A similar app is called SmartTubeNext.
https://smarttubenext.com