Apps can force you to update in this manner. The app my company created checks the latest version and directs users to the App Store to update. This helps ensure new features releases do not break existing items in apps that cannot use the new feature.
If you are unsure, you can go to the Play Store or the Freetrade website and click to download the app there. It will soon tell you if you already have it and needs updating. This of this like if your bank calls you and you don’t speak with them but instead call them back.
It’s unlikely Freetrade will be able to help with your phone or understanding if it can be stored elsewhere. I would suggest as above you delete some apps. You can always reinstall these if you end up saving space.