Hyperlinks can be just internal links.
The bookmark name is prefixed by # instead of a full URL or else select Document option and then you can browse for bookmark
This is a full external url:
https://www.corvidspress.com
This is an internal url for bookmark ch1:
#ch1
When the ebook is created the # will be prefixed by the name of the automatically created chapter file both in the links and the anchors.
I've no assurance that "cross reference" feature creates the second back text, url and bookmark correctly or that it converts properly. I've not used it for years in MS Word or LO Writer. I see no advantage to it.