Seems to be working now, before to test I was sending an email to myself using my own gmail account. Ordered a Pizza from Dominos and the order confirmation email showed up on my watch when I checked for mail.Gmail has never worked for me, I’ve given up with notifications and forward everything to my iCloud address. Notifications from that are very prompt.
So then I sent an email from my new iCloud account to my gmail account and that showed up on the watch too. Still well worth having the iCloud email account as I say had no gmail recovery account before and wasn't interested in a Microsoft one.
I'm not really bothered about having emails pushed to me as soon as they arrive, gmail on my Samsung Galaxy S25 does this anyway.