Unable to Edit Page Source Code to Put In New GA4 Tag Code Manually

Hello! After following the steps to connect the Universal Analytics and GA4 property together, one of the next steps is to manually insert the tag code for GA4. I can access the page code after clicking view “View Your Store”, right clicking, and then pressing “view page source code”. However, once I access the page code, I’m unable to copy and paste the tag code into it. How do I edit the page source code?

Thank you.