The error says it can’t read the sitemap cause of an error when opening it, and it refers to guidelines. I have another nearly identical website, where there is no errors. Sitemap look identical except root domains.
Therefore I thought DNS could be it yes, but Webflow shows no issues with DNS settings.
@Kjetil-G - Since your sitemap loads I would make the assumption that this is a temporary condition with Google. Wait a few days and it should resolve itself.