Image preview, two requests for the "toggle button": 1) add tooltip and 2) allow app settings to control the default state

For all's convenience, please use English to fill this issue.

Is your feature request related to a problem? Please describe.
not applicable

Describe the solution you'd like

1. Add tooltip for the "toggle button." (I don't know what to call it even when filling out this form!) :D
2. Add an option under the app settings for the default "toggle button" state ("normal" or "alternate", "off" or "on"; see discussion below) when I hit the space bar to preview the image.

Describe alternatives you've considered
not applicable

Additional context
Example preview of a .png file, with red arrow added by me to point to the "toggle button." For the sake of discussion, let's call this state "normal."

Here's what happens when I click on the "toggle button." Let's call this state "alternate."

I installed Quick Look specifically to help me determine whether images have a transparency layer or mask or alpha channel (not sure of the correct terminology). For this reason, if my suggested feature is implemented, I would change the default "toggle button" state to be "alternate."

Note that maybe "normal" and "alternate" are not the appropriate words to use; maybe "off" is the default when the app is installed and I would be changing it to "on". Hope that makes sense.

Start by locating the image preview UI and its toggle button, then trace how app settings are defined and loaded. Confirm how the button switches between normal and alternate states, add a discoverable tooltip and a persisted default-state option, and verify both settings values when opening an image preview.