Ignore my question. The following works (had to look at the source, which I should have done in the first place, of course <blush>):
#+cite_export: basic numeric nb Thank you and back to your normal programme ... ;-) -- : Eric S Fraga via Emacs 28.0.50, Org release_9.4.6-625-ge7454c : Latest paper written in org: https://arxiv.org/abs/2106.05096