Can’t see images in posts after migrating site to subdomain

I’d use a Search/Replace plugin (I like “Better Search and Replace”) to look for any old URLs. (That plugin has a ‘test-but-don’t-change’ option.) If you find any old URL, use the same plugin to replace with the new URL.

Although you can use SQL commands to make the changes, the plugin has always worked better and faster and easier for me.

I’d also check the URLs for the media item on the Media page. Might be that the old URL is in there. The plugin will fix that.