Latest Rhino 9 WIP, the cursor goes to nirvana after entering a key and pressing TAB.
This was the youtrack for a fix a few weeks ago: https://mcneel.myjetbrains.com/youtrack/issue/RH-87722
And the related topic about Attribute user text: https://discourse.mcneel.com/t/attribute-user-text-cannot-paste-key-or-value/
TAB works fine for Attribute user text