If you’re looking at the page source, it won’t be between the head tags. Do a search for your adsense publisher code in the page source and see if shows up - it should be about 3/4 of the way down.
Yes, it will need an ad to have something to display on your site, but if the domain hasn’t been approved yet by Google, I doubt you will see anything except a blank spot.
You do not need a theme component for AdSense or Google Ads (DFP) to work.