Form document: Check boxes - background changes to black when exporting to PDF

Check Boxes and buttons look okay and work ok in Writer, when I create them. But as soon as I export to PDF the elements change to a black background and don’t appear to be selectable.

Check Box properties - background is set to default. If I change the background color it changes in the Doc and PDF but I’m unable to change (or see any change) when I select the check box (no tick displaying).

Here’s the PDF settings

I came across the same thing. For some reason the default background is black. Go to the control properties and scroll down to find background colour and change it to white

Bug 150786 - Exporting form controls to PDF gives different results depending on system dark mode has been resolved for 7.4.4 and 7.5 and later. The solution there is to upgrade LibreOffice

If you have a version of LibreOffice later than either of those and are seeing this issue then please make a bug report, How to Report Bugs in LibreOffice - The Document Foundation Wiki