I am using wordpress with Elementor Pro and the plugin Element Pack Pro (this plugin has an iFrame widget where you can select "auto height")
When calling a domain from the same domain that the iframe is on, the auto-height works perfectly. However, when calling from a different domain, which is a sub-domain (NOTE: I DO own this sub-domain) then it will not auto-height.
under the auto-height toggle, it says: Auto height only works when cross-domain with "allow origin all in header"
I've submitted this info to the plugin developers, however after several weeks they still do not have a solution.
I have not tried anything on my end, please note that I have extremely basic knowledge of JS, PHP, etc and would need detailed instructions on ideas to test.