You can’t personally contribute to a 401k beyond the limit, even after tax. Your employer can add extra via match or profit sharing contributions. What are you talking about?
For 2026, the 401k limits are $72,000 overall, and $24,500 for pre-tax employee contributions.
Assume an employer who matches 50% up to pre-tax employee contribution max, the result is this:
$24,500 pre-tax employee contribution
$12,250 employer match
This leaves $35,250 to the $72k limit.
Roth MegaBackdoor enabled plans allow the employee to put $35,250 of _after tax_ contributions in to fill that window, and to convert them to Roth assets. They can even be rolled out into a Roth IRA while the 401k is still active.
I have no clue why you think this relatively common plan option is, somehow, impossible.
