I can't download images from the internet when I clicked on save the file manager doesn't open, and I can't download the images
Have you made any modifications to your Desktop that may help us understand why? Such as changing to a different File Manager (I Use NemoFM for example).
Do you use a Download Manager?
Which Browser are you using?
Sounds more like a browser problem than a file manager problem.
Make sure that the file manager window doesn't open on another monitor or even under some other window. You can press Ctrl+Alt+Tab to switch between different active panels like dialogs as shown here:
Very good suggestion.
On MacBook, it can happen where the system thinks that there are Two Monitors even though there is one monitor and it opens the Save As dialog on the other non-existent monitor. A configuration change is needed to resolve it.
are downloads using the file manager or are they going directly to the default path? you can usually select which option you want in settings.