Newly created email in iCloud is coming up as Gmail.

iMac Sonoma 14.4.1: iCloud email account is periodically producing a new email linked only to the gmail account. About 60% of the time, there is no way within the email message to change to the iCloud account. This happens both with a new message and a response to an inbox message. It started about a week ago and is intermittent. Sometimes the drop down arrow allows me to select the iCloud account, sometimes it only offers to hide my address from the recipient. I saw that someone else had this question about 2 years ago, but I did not find an answer from that inquiry.