Just noted that the GUI for Gramps Web is built with the Flist Lit toolkit, while Gramps uses Gtk+ (GIMP toolkit).
One of the major visual differences that make Gramps appear alien in the OS is when adding Media. Gramps the Gkt+ File Chooser instead of native File Choosers. The Gtk+ File Chooser has a different look, bookmarking capabilities and support of Environmental Variables.
The Gramps Web user guide does not include a screen capture of the Add Media File Chooser. Is there a Flist Lit File Chooser or does it use the native File Chooser for the device?
https://www.grampsweb.org/user-guide/media/