I have the problem that I don't know how to see how long, for example, with the Enchanted Apple, the shield effect can be seen. I've only been playing Minecraft for two weeks and I'm not very familiar with it yet.
On which platform
I think you can only see this if you have the Minecraft Java Edition.
In Java you can see in the inventory how long this will go.
Okay and not in windows 10 version?
Windows 10
I also have this version and it is not displayed for me so I believe that it is unfortunately not displayed for others either.
You probably activated the crafting book.
Then you no longer see the effects because it is masked.
Open your inventory (e) and click on the green book under the crafting field. Then it will fade out and you should be able to see the effects again.