This is only possible via an intermediate version of EVO V13!
I see with you but no registration of V2019.3!

Hi Matt!

Please find here the procedure to convert your files from version 10 into the new one:

1- Download WebSite X5 Optimizer from the following link:

https://www.websitex5.com/download/optimizer/1.10.0/WebSiteX5Optimizer_x86.exe

or

https://www.websitex5.com/download/optimizer/1.10.0/WebSiteX5Optimizer_x64.exe

2-Import the project into Optimizer

3- Choose the option "no optimization" if you are still going to work at the project

4-You will then be able to import the project in version 2021.4.

Thanks! Kind regards.