@John_RM_70 Aha! The key was renaming the BIOS file to dragon32.zip! (From d32.zip.) Many many thanks for that. Now I have the Dragon OS screen showing, if I could only figure out why the A key won't work (leaving me only able to type "CLODM") I'd be sorted...
Please do not post a support request without first reading and following the advice in https://retropie.org.uk/forum/topic/3/read-this-first