Trying to Make Static Classes Into Extensions of Unity's Classes but Getting Errors

I've had a nice little set of methods that I've created over the years and have had them in static classes so that I could call them from anywhere. The only (slight) downside to this is that I have to set my data equal to the class.method. I'd like to just use the method directly from the current object. What I've been doing is:
What I'm trying to do is:
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Trying to Make Static Classes Into Extensions of Unity's Classes but Getting Errors