Place the laptop behind/below the TV, hook it up via HDMI, install whatever software you want on it (I use plain linux and VLC, but you can install Jellyfin and use the web interface if you want to), use a bluetooth keyboard/mouse combo to control it. You can enable USB wakeup if you want to minimize power usage, but you have to make sure the keyboard is plugged into a USB port that's powered when shutdown then (if that's even possible given your config).

I had an Asus TP500Ln that I only just retried, it lasted me 10 years as a TV box, always more powerful than fire sticks/actual tv boxes.

Replaced it recently with a 4 year old laptop.

I simply install Ubuntu, plug in the TV through HDMI and keep the charger plugged in all the time.

Then I can install stremio, Kodi and any other streaming apps I like. Technically I could also set up some retro games.