Preview images in dialog window

I'm searching for a solution to change the view of icons (images) within the Ubuntu built-in file manager in dialog windows.

Image of dialog window:

Example: Click on "upload images" on eBay --> dialogue window opens --> after choosing the folder with images I would have to click each image to see it bigger in preview, but with 700 images in the folder I would have to click a lot!

I know that clicking an image will show a preview on the right-hand side, but with 700 images this is a long process.

I set Dolphin as my default file manager on the recent Xubuntu 21.10. via:

xdg-mime default org.kde.dolphin.desktop inode/directory

but the file manager within dialog windows still seems to be Nautilus with no way to resize the preview icons in the folder.

Solution found:

Intsalled kde plasma and then added in ~/.profiles at the end:

GTK_USE_PORTAL=1

The filepicker is now Dolphin.

Works fine and without bugs.

Solution is explained here: https://itectec.com/ubuntu/ubuntu-kubuntu-18-10-how-to-change-this-file-picker/