"Open in new tab" toggle doesn't work for menu links
This is a bug report. When adding an external URL item to a menu, the link always opens in an external tab, regardless of whether the "open in new tab" toggle switch is active or not.
Glancing at the HTML, it looks like the link always gets the target="_blank" attribute, which causes this.
The toggle works correctly on other URL links (e.g. on images)