You’ve set me on a good path and I found a few related articles:
https://www.isitwp.com/set-default-attachment-display-settings-alignment-link-size-wordpress/
https://github.com/WordPress/gutenberg/issues/10173
Unfortunately, none of these work, either. Apparently, I’m not the only one with this problem, either.
Hopefully there is a fix soon ??
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