Why is my internal storage space constantly so low on my Samsung Galaxy A12 phone when I use an SD card?

My Galaxy A12 is always notifying me to delete unused files to avoid running slowly\apps not working correctly due to low internal storage space. I've moved any\every thing that's able to move to my mounted SD card. I still have low space & all of my music, pics, and certain apps are moved off my internal storage to external storage. I've tried Files By Google which seemed to help a little but I can't get my internal space low enough to download again.