Sibelius’s warning is nonsensical, I’m afraid. Dorico is exporting MusicXML 3.1, the latest version. Only the very latest version of Sibelius, 2020.4, knows anything at all about MusicXML 3.1, despite MusicXML 3.1 itself being more than two years old as a format. So that warning is immaterial.
However, it is the case that Dorico’s MusicXML export does not currently include tablature information. That’s something that we plan to address in a future version of the software.