Hi there –
I too am trying to use Google Trends graphs via the “standard” method described below and the graphs don’t appear in Safari – but do appear in Chrome and Firefox.
1. Go to Posts > Add New and add a title.
2. Go to https://trends.google.com/trends/ and enter a search term.
3. Click the embed option and copy the HTML provided.
4. Paste the HTML into the Text tab of the post body.
5. Publish the post.
6. Check the post and note whether or not the embedded Google Trends graphs work as expected in Safari.
This issue has actually been going on for at least a year.