The third benefit of the Telekinetic feat states (Tasha's Cauldron of Everything, page 81):
As a bonus action, you can try to telekinetically shove one creature you can see within 30 feet of you. When you do so, the target must succeed on a Strength saving throw (DC 8 + your proficiency bonus + the ability modifier of the score increased by this feat) or be moved 5 feet toward you or away from you. A creature can willingly fail this save.
Can someone target themselves with this ability of the Telekinetic feat, choose to fail the save, and push themselves out of melee range, thus causing the same effect as a Disengage action?
I am unsure. The wording seems to suggest you can; however, the phrase "or be moved 5 feet toward you or away from you" seems to indicate you cannot target yourself with it.
Best Answer
You cannot be moved "away from you".
The motion of the telekinetic shove is defined relative to you:
"Toward" and "away" denote a change in the position between two reference points – "toward" meaning the distance between you and the target is decreasing, "away" meaning the distance between you and the target is increasing.
However, your position relative to yourself is constant; you can neither decrease nor increase the distance between you and yourself (this is the very first axiom of metric spaces). So you cannot use the feat to move yourself.