There has been a bug in the WordPress core that strips target="_blank" from any "a href" links added to the user's "Biographical Info" field.
The links work fine, but they just won't open in a new tab when clicked since target="_blank" is automatically stripped from the link. This has been an issue for years now.
To fix it, simply add the code given below to your WordPress theme's
I hope this fixes the problem. If you still have any doubts, then feel free to drop a comment below.