All options are set via environment variables. You can also put them in a .env file in the directory you run the command from (or one of its parents); variables already set in the environment win.
A boolean is true when set to true, 1, yes or on (any case); any other value is false, and an unset or empty one takes the default.
Remove external links, keep what they wrap (text, images, markup)
REMOVE_EXTERNAL_LINKS_REMOVE_ANCHORS
false
Delete external links together with what they wrap. Overrides REMOVE_EXTERNAL_LINKS_KEEP_ANCHORS, and deletes contact links instead of pointing them at #
MAKE_INTERNAL_LINKS_RELATIVE
true
Convert internal links to relative paths. When false they keep pointing at the original site's URLs instead of the saved files
With both external link options false, external links stay and point at the live site. Button links (btn, sppb-btn classes) and links in icon groups are always kept.