if i not mistaken, i usually making hype website with iframe, (in 2017ish) i put some contact form, google drive folder, or even wix page into iframe. but i can't do that now.
why only few website can show using iframe now (oct 2020) ..?
am i miss something?
i want to put these google sites into iframe as "news section" so my friend can easily update it.
https://sites.google.com/view/pge-latest-news/home
The issue will likely be that google does not allow for the site to be loaded in an iframe.
many sites do this to stop misrepresentation etc.
What @MarkHunte said is correct; please see that the web developer console will log an error like:
Refused to load https://sites.google.com/view/pge-latest-news/home because it does not appear in the frame-ancestors directive of the Content Security Policy.
Beyond your specific needs, this is a common problem since the first "test" site most people use for iframes is google.com 
.