Generated Sitemap contains URLs/Links from external sites

[tradmangh]

MetaSEO version: 3.0.0

TYPO3 version: 8.7.30

Sitemap shows URLs with /?fbclid=7w37rg9rzgfw7efrg9w...
These seem to come from our facebook-page because the indexer follows external links on the website and interprets them as internal links and adds them to the sitemap.
How can the indexer be influenced to not follow external links or exclude certain paths (other than switching the caching off)? Couldn't find any hints in the documentation.
Blacklisting all those wrong URLs is not really an option, because this issue also causes the sitemap generator to run for hours and create external traffic.