Lots of stuff in Junk, though I can't see anything that looks like HMRC from about the date submitted. I did receive emails on the 3th Dec, for the short confirmation code and for the Government Gateway ID needed for the login.
Logging in gives me:
File a return menu
1. Welcome
2. Tell us about you
3. Tailor your return
4. Fill in your return
5. Check your return
6. View your calculation
7. Save your return
8. Submit your return
Provide feedback
Tax return options
How to pay
Fill in your return
Section skipped
!
Warning
You must complete the sections up to '4. Fill in your return' in order. After '4. Fill in your return' you can skip any section using the left hand navigation links.
1. Welcome
From 'Welcome' you can only navigate forward to '2. Tell us about you'. This is because we need details about you before we can create your tax return.
2. Tell us about you
From 'Tell us about you' you can only navigate forward to '3. Tailor your return'. This is because we need details about your income before we can create your tax return.
...
I have put the menu in blue, and since it seems I need to get to the Tell Us About You page from the Welcome page, I clicked on that, which is the page where I get the "
The 2019 to 2020 tax return for ME was successfully submitted and was received by HM Revenue and Customs at 15:27 GMT on 29 December 2020."
But there is no link to get to the Tell Us About You page.
If I go to the View Your Calculation page it says they owe me £4!