Most Apple native applications place on the clipboard text in a custom RTF format.
This RTF test is converted by electron/chrome into HTML and from HTML to markdown by Obsidian.
For unknown reasons, the source RTF placed on the clipbaord by the Apple apps includes spurious spaces or paragraphs between lines, even if a paragraph was not present in the source material. These error trickle down to text that gets paste into Obsidian.
Obsidian should recognize the custom Apple RTF format and actively try to fix it during the paste process.
Current Workaround
Paste without formatting