On the site you advertise Popup widget to Google Site | Add Popup extension on you website [2023]
Please remove any suggestion that you can add a pop-up to Google Sites for the following reasons:
Google Sites places Embed Code in a sandboxed iframe that blocks pop-ups, so Google Sites cannot be cajoled into having a pop-up.
The gadget doesn’t offer any kind of code to actual pop-up, it’s simply a way of creating a pre-defined piece of HTML.
Hello @Steegle! We are so glad to see you in our fast-growing Community! Welcome 
I am terribly sorry for all the frustration caused by this misinformation 
Please accept my sincere apologies
You are absolutely right! Unfortunately, all popup and floating elements of the apps (including Popup) are being converted into iframe format, which causes incorrect displaying. For this reason, we’ve made a special notification:
We also have a lot of static widgets. If you get interested in them, I guess, Banner widget could be an option in this case.
A huge thanks for sharing your feedback with us 
If any questions come up, please do not hesitate to contact us. We are always happy to help!
