If the tab s4 runs the games you play and movies well, I don't see why not to keep it. I was bought a tab s7+ back in december 2020. No regret keeping it over my ipad air 2020. Its a great tab with an amazing screen to watch content on, plays games fine. If you did upgrade to one of there latest tabs, I don't think you would be disappointed.
It should be usable still for a while until the version of Android is no longer supported by Google. At that point any TV or film streaming services will also drop support for it. So depending on the state of the battery you may get 2 more years usage from it yet