I think most people who have a large collection of movies have a NAS to store everything. I built mine with leftover PC parts after upgrading my main PC. Started by just throwing some extra hard drives into my old case, then incrementally upgraded it with used server parts from ebay, bigger hard drives, etc.
You'll typically want to use something like Plex or Jellyfin to serve the movies to whatever devices you're watching on. Then you'll get into docker and the Radarr/Sonarr/*arr stack...