Early 2009 iMac, Cannot upgrade further than El Capitan 10.11 - what will happen with iTunes?

Hi,

My iMac is old, (early 2009) and it cannot be upgraded further than El Capitan 10.11. What will happen with my iTunes if I can't have Catalina to upgrade? I have 21,000+ songs in my library which includes songs I purchased and songs it took years for me to rip from CD. I also have a substantial amount of iTunes credit I've racked up over time. Will I not be able to use my iTunes credit and purchase songs anymore? I can't really get a new machine right now, and I'm hoping I can still use what I have somehow!