LibreOffice Push-Button hyperlink not working

[Martin1001]

Why does Hyperlink-2 below work, but not Hyperlink-1?

I start in a LibreOffice document (Version: 6.0.7).

Hyperlink-1
Form Controls > Push Button > drag rectangle.
Right click > Control > Properties
Action = Open web page
URL entered
Background = red, Font = white
close Properties

Hyperlink-2
I then create some text containing the word 'here',
select it, Insert Hyperlink, select 'web', enter URL

Save
Export as PDF

As the file is being saved to PDF, the white font on the LibreOffice Button changes to grey.
Open the pdf > The pdf Push Button does not work; clicking on 'here' does work.

Returning to the LibreOffice document > select Push Button > Right click > Control > Properties
Action = Open web page (so no change there)
but URL is now blank
Background = red, Font = white (but it isn't, it's now grey)

What am I doing wrong in setting up the Button (Hyperlink-1)?