my guess is it is a linux function. The dialog used in Windows is a default Windows dialog with options to switch the view to the standard windows views of small and large icons, list, tiles, details etc.

Based on that I would assume KDE and gnome both have a "standard file open dialog. A little research indicate they do. KDE here https://docs.kde.org/trunk5/en/applications/fundamentals/files.html

Gnome here https://developer.gnome.org/gtk3/stable/GtkFileChooserDialog.html

It appears KDE has an option Gnome does not.

You say you are using Mint, so perhaps this will help. https://forums.linuxmint.com/viewtopic.php?t=42709

Thanks for your suggestion, Matt. I should have posted that I already went into the file display and set it to thumbnails. So If I open the file app and go to my "pictures" directory, I'll see thumbnails.

But if I am in Thunderbird and go to "attach" a picture, all I see is the file names - and no way to convert the display to thumbnails.

Also, I tried to find "nautilus" on Mint but it does not show up as a program.

I'm including a screenshot of my "picture" subdirectory showing the thumbnails.

Here's a screenshot of what I get on Thunderbird when I go to "attach" a picture.