Hide pages from sitemap

Hi all, I have a collection of pages on my site which are accessible via direct URLs emailed out to customers using a Zapier integration (e-receipts!).

I have already no-indexed these pages in robots.txt but would also like to outright hide them from sitemap.xml - is this possible somehow? Are they already hidden from the sitemap by virtue of Disallow in the robots file?

Any help is appreciated, thanks!