How do I free up storage on my iPhone 11 without downloading an app?

You don't need an app to remove things from your phone. You delete things you don't need or use, such as Photos, Music, Apps, Files, Email, Messages, etc. That's pretty much the only way to free up space. You can also make sure you use optimized storage for your photos, by going to Settings > Apps > Photos > Optimize iPhone Storage

Just delete photos you don’t need and then go to the deleted pile or whatever and delete all of them I did it and really does free your storage