Gallery Panel (Properties,Custom Objects, Leases)

A file field must already exist to select in the Gallery panel configuration step.

To create a new file field:

Go to Settings > Fields
Create a New Field. The field type selected should be "Related To" - "File"
Select "Any" in the Allowed Type dropdown. (The gallery panel will support displaying .pdf file types)
Select the checkbox for "Multi Select" to allow users to enter multiple files into the field which will display in the gallery panel.
Only 1 field can be selected to configure the gallery panel so be sure to select the "Multi Select" checkbox to include multiple images/pdf files in the gallery panel.

The file field needs to be added to a layout for users to be able to add files into the gallery.

Ensure the file field has been added to the Layout.
Select Edit Layout.
Select Add Panel
Select Gallery from the list of Panels
Select Save
Select the field dropdown in the Gallery panel
Select Create New Gallery
Upload a photo to the file field by selecting the + icon within the field.
Use the device file explorer to select the file and save the changes on the panel.
The uploaded file will now appear in the gallery panel. A refresh may be required.

Curate custom gallery panels in Properties, Custom Objects, and Leases Layouts to show specific images and PDFs within the layout tabs.