Update.
Found a handful of other posts on reddit and elsewhere that suggest this isn’t an unheard of issue.
still have not resolved anything.
This webpage (Pasted screenshot images fail to display) suggested a few troubleshooting tips:
I’ve found that the problem occurs also in a Sandbox vault.
I turned on restricted mode; made no difference. So not plugin related.
No snippets.
I’m running Obsidian Version 1.5.3 (Installer 1.4.16).
IDK if any of this makes sense to anyone (way over my paygrade), but this talks about a “PNG file signature spec” that could be a problem: Pasted Screenshots images fail to display.
Not making any progress at all.
I can paste jpg files, images from the internet, older or renamed png files with no problem. But as it stands there’s something about these specific png files that makes markdown mode unusable for me; I’d have to manually modify those screenshots in finder before pasting.