Krokiet 'Add' does not give select folder dialogue on Linux Mint 20.04 XFCE

[tallishpaul]

System is Linux Mint 20.04 (Ulyana) XFCE. New install of Krokiet 8 using linux_krokiet_gui binary from Github.

If I click on 'Add' for 'included directories' to choose folders to search, I don't get a dialog box that has "select folder" - like I have used on a Windows 10 install of Krokiet on my laptop. Instead I get an 'open folder' dialogue, see attached screenshot. I can't select, only open a folder, with no return to Krokiet and not populating the 'included directories' list.

Looks neat on Windows, but it's Linux that needs decluttering!