There is the desire to make iframes load lazy. See #3167034-23: Leverage the 'loading' html attribute to enable lazy-load by default for images in Drupal core → as an example. Currently, there is one iframe usage in core, but lots in contrib.
Continue to use the existing html tag approach. Add a feature to the oembed field formatter to toggle lazy load on/off.
OEmbed field formatter supports eager or lazy loading of resources i.e. Youtube videos.
Fixed
10.1 ✨
render system
Not all content is available!
It's likely this issue predates Contrib.social: some issue and comment data are missing.
I have unpublished https://www.drupal.org/node/3264760 → as the iframe render element did not make it into core. I was quite confused when it was not working after I found the change record. Took me quite some time to find out the change was never released as described in the CR. :-)
@ricovandevin, thanks for doing that and for commenting!
I did miss the earlier comment to delete the change record. The CR is now deleted.