It mentions the may capitals that Muslims set up in various divisions of Syria and its southern districts in Palestine - and none of them are Jerusalem.
Ramlah is in Israel, and Palestinians never talk about how historically important it is for them. Wikipedia in Arabic doesn't even mention that Ramlah was ever a capital city, although this book mentions it repeatedly from multiple sources.
And just in case you aren't clear, it is stated flatly that while Jerusalem had importance for Muslims (and there was an attempt once to redirect Muslim pilgrims from Mecca and Medina to go to Jerusalem instead,) Jerusalem was never the political capital of any Muslim entity.
