Strikethrough not working

The strikethrough function is currently greyed out, making it unusable which is a major inconvenience when editing.
I’m running Catalina on my MacBook Air, but I have used Scrivener, and the strikethrough function, since moving over from Mojave to Catalina so I don’t think the change in os can be the problem.

For info, I’ve had Scriv for Mac since about summer 2019, and moved over to Catalina around autumn time.

Can anybody help?

Strikethrough is only available when you select previously written text. You can’t type struckthrough text. Does that explain it?