Plasma discover updates page blank (5.20.3, with frameworks 5.74 and Qt 5.15.1`)

[Rik Mills]

Plasma discover updates page is blank when updates exist:

Version 5.20.3, with frameworks 5.74 and Qt 5.15.1

Discover updates page: https://i.imgur.com/8LpPCEW.png
Error on clicking to navigate to that page: https://i.imgur.com/jVTCCdy.png

It has been suggested that official required kirigami 5.74 is not
actually new enough?

Regards,

Rik