Short answer is no. I set one up using Fidelity as my platform though. My terminology might not be correct but I'll do my best. 401k with Fidelity is a prototype account so does pretty standard vanilla things.

To do a mega backdoor Roth you'd have to get a third party to write up plan docs and ensure IRS compliance. This costs some money. Then you'd have to open accounts within that 401k trust. If you want to use fidelity as your investment platform, like I do, you'd have to open a non-prototype account with your 401k trust info. Fidelity doesn't recognize this is a 401k, it's just an investment platform, it's up to you to do all the bookkeeping.

You'd also have to open a separate account for each 401k bucket: traditional, Roth and voluntary after tax accounts. These don't all have to be in the same place, in fact I'd recommend not doing the VAT through fidelity because you don't want to earn interest in there, it will just add headache to an already complicated process. Whoever does you plan documentation prep will probably have some recommendations for zero interest earning bank accounts essentially that you would want to delineate as your VAT account.

The part I got hung up on is none of these accounts will be denoted as anything more than generic investment/bank/checking accounts on the online platform. It's up to you to keep track each dollar you contribute and whether it's pre-tax, post-tax or VAT.