OK, thanks! Just sent the patch. I realized in my original one (https://list.orgmode.org/20220228140750.75761-1-dafydd.lu...@gmail.com/), I'd also gotten rid of the with-temp-buffer in ox.el as long as I was switching to write-region, because write-region can write a string directly, but as that's not strictly necessary, I didn't include this change in the updated patch, just the ox-odt.el stuff. Hope that's OK.
David