It does not work in an open links in a new tab

A check mark in the item “Open external links in a new tab by default.” worth. Links do not open in a new tab.

Please take no offense, I only want to make sure you understand what that setting does.

That sets that as the default preference setting for new members that register after and while you have that setting enabled.

Have you checked as a new user (ether an alias account or impersonating) that the profile preference setting is checked and that external links in posts do not open in a new tab?