Using New Outlook on Windows for personal email, calendar, and contact management
This did not work for me. However, I did find a solution that did work. Its not a permanent solution, but will help in the short term. At the top right hand corner of you new outlook app, there should be a switch called "new outlook" and will be switched on. If you switch it off, you'll be taken to the old outlook where you can update you signature and the formatting will remani. You can then switch back to the new outlook and your signature will stay.