The storage information in the general system settings will show you how much the app itself plus its configuration data plus any data you’ve created with the app.
If the app has templates or other configuration data, it is likely stored in the application support folder inside one of the library folders your data that you created is stored wherever you stored it.
Any data you created will be stored wherever you stored it.
if the app required an installer, you need to use the apps uninstall are provided by the developer. Any other app can just be drag to the trash, but you will still have to delete your data and any application support data.
Unless it’s some app that requires a lot of video or image templates, or game, save data, the data stored in the application support will be minimal