I just tried this but unfortunately for me it didn't work. The temporary user did have access, but I still do not. I am hoping I can find a way to get it working without a re-install (that's a lot of work for me).I contacted Apple Support and went through numerous troubleshooting steps, and finally they told me to create a test user (macOS user) and sign in my Apple ID in it, after doing that I was able to use Hide My Email in the test user, then they told me to sign out my Apple ID in the test account then logout the test user. After I log back in to my main user, I was able to get Hide My Email working. Apparently even the Apple Support Specialist doesn't know why that fixes the issue, but it works for me and I believe that worth a try.
You're correct, it doesn't have a toggle box. But the problem I and other users are encountering is that when you click 'Options' you get the 'Not available' response.I don't believe the option is supposed to have a toggle on box. You are supposed to tap on Hide My and then create a new email address that you want to use to hide your real address. Once you have created your hide my address, using it in place of your super secret email address will still forward to your secret email. Hide my email has been working for me.