@robi hmmm, that's a good question.
I was under the impression that some text is mandatory.
But having tried it, Mastodon certainly allows it.
And the RSS feed looks like this :
{
"title": "xxxxxxx: “”",
"link": "https://xxxxxxxxxxxx",
"pubDate": "Sun, 26 Sep 2021 19:56:22 +0000",
"enclosure": {
"url": "https://xxxxxxxxx.png",
"length": "14690",
"type": "image/png"
},
"content": "",
"contentSnippet": "",
"guid": "https://xxxxxxx",
"isoDate": "2021-09-26T19:56:22.000Z"
},
So it works.
Although my n8n workflow to crosspost to Twitter would likely break, but I will try that later when I'm feeling braver.