I type "c, " and I get "checked," instead of class template, I remove some characters with the backspace when I have "c," + space I get the template.
It's the same for all class template.
See the video.
There are two options on the "IDE\IntelliSense" options page at present.In your case, you need to choose the "Always expand templates" and "Send the trigger character typed to the editor" options to be able to expand the "c," template while IntelliSense is active.
The attached screenshot illustrates how to do this.