Buy physical media (CDs DVDs and Blu Rays) when possible and burn your own as backups when you get stuff digitally.
Set up a computer as a Linux-based server running 24/7 with Plex or Jellyfin or similar. Even most consumer tier motherboards these days can support many sata hard drives, and you can get ones that are 10Tb+ fairly inexpensively. Set them up in RAID of some form to avoid losing data.
It’s good to have a remote backup as well but that can be expensive and more complicated.