ALARM!!!
You copied and pasted something without understanding it.
Always copy by hand making sure you understand every bit.
The bit between brackets in your item definition is a group
Items can belong to groups
You either need to create a group by that name or get rid of the group in the item.
BUT because your sitemap is looking for that group, because you just copied and pasted code, youl will need to create the group.
So your new items file should be:
Group GF_Sonoff_RF
Switch GF_Sonoff_RF_Button_1 “Button 1” <none> (GF_Sonoff_RF) { channel=“mqtt:topic:9770d4aa:sonoff:button1”, autoupdate=“false”}
And please use the code fences when posting code, thanks