Resolved by author
Resolved in: SEOPress 6.5
Overview of the issue
SEOPress is not currently compatible with the language URL format to display A different domain per language. It does not currently work to create a sitemap for each domain, however, SEOPress is aware of the issue and plans to make it compatible.
Workaround
There is not an available workaround for this issue.
You can change your URL format to Different languages in directories or Language name added as a parameter, and SEOPress will create one sitemap that includes all pages in the different languages.
Next steps to resolve this issue
We’ve spoken to the SEOPress team who are aware of this issue and will look to investigate a solution together. There is currently no ETA on this effort, but we will update this erratum as and when we have more news. If this feature is important to you, please feel free to let the SEOPress team know via their support forums (for free or PRO version types) or Facebook group, and we can try to push this forward together sooner.