In September 2023, Safari 17.0 on macOS introduced a change to the element where you can now add an
element inside it to create visual breaks between options. This feature, which was previously supported by Safari over a decade ago, has gained attention recently. To implement this feature again, some modifications had to be made to the HTML parser and corresponding semantic and conformance changes were needed. It’s important to note that the separators created by the
element are not announced by assistive technologies like VoiceOver. Overall, this update provides authors with more options for visually separating options in the element.
https://webkit.org/blog/14933/bringing-back-horizontal-rules-in-select-elements/