How can I keep multiple Safari windows with different Gmail emails open on Mac?

I use Gmail in Safari on my Mac Studio. I do not use the Mail app. I have only one gmail account. I like to open multiple windows in Safari and work on different emails at the same time in the different Safari windows. Sometimes I'll copy something from one email and then switch to gmail on another screen and paste in the information into a different open email. I had been doing this for years. Then about a year ago, every time I started in email in a Safari window, all the other open windows with gmail open switched to that one email, and when I started working on another email, all the other open windows with gmail switched to that one. I could not keep different gmail windows open. A few months ago, it suddenly switched back and I could work on different emails in different safari windows at the same time. I have no idea if I did something to make this happen. And then just as suddenly it switched back, where every time I start working on one email, that email appears in all my other open Safari windows that are open to gmail. I went into Gmail Settings/Inbox but I couldn't find anything that applied. Any ideas on how to fix this?

[Re-Titled by Moderator]