looking at the release dates i would assume that the following versions 5.21.6 and up are compatible.
They are not working. I cannot convert the 4.8.11 version into any of the Mx5 versions.
Probably the issue is that your used Mx4 version is newer than the Mx 5 version used.
So the MX 5 version is not familiar with the Mx 4 version.
This needs to be fixed by Mendix. Thus contact support: https://support.mendix.com
Mendix will do a fix for this in a next release perhaps 2 months.
For anyone else who visits the page and is facing the same issue in trying to convert a 4.8.11 version to Mx5 there is a hack to resolve the problem
Download your app from the team server.
Open the .mpr file in a hex editor (I used Notepad++ with Hex plugin) - change the value of 0f 4.8.11 to 4.8.10 - don't worry about the other versioning numbers leave them as is - its around line 16 in the file - save the file
Do the same with the base_ver file within .mendix-cache
You then do a search in files within the .svn/pristine folder looking for 4.8.11 - I used Notepad++ again. There should be one file in there with it. Edit that as well and change to 4.8.10.
You should now be able to open the project form a 4.8.10 version of the Modeller - Once it is open do a Team server commit of the project.
You should now be able to open an Mx 5 modeller, open the project and be presented the conversion wizard.