I deleted the UK Dividend section of my unsubmitted, then re-entered it. The same problem - it again exactly doubled the amount I had entered when making the tax calculation. I phoned HMRC and the best they could offer was to submit the return, and phone them again to sort out what I and HMRC know would be an incorrect tax bill. All other elements of the self-assessment went into the calculation correctly. Only UK Dividends seem to be at fault.
After completing self assessment form on-line, the tax calculation showed exactly double the UK Dividend I had entered. Hence tax calculation is grossly over-estimated. Anyone else experienced this for 2021/ 2022 self assessment?