Yes, but note Roth 401k dollars or Roth dollars via conversion in previous plans cannot go into the DL 401k. That still allows for the Roth backdoor IRA. Previous Roth dollars from a 401k would just roll to your RIRA.

The Mega is also 401 after tax dollars and has zero bearing on previous IRA balances. To “clean the deck” for the standard backdoor RIRA you simply need a “0” traditional IRA balance between tax years. That applies to each filer individually in the event you are also planning on the spousal contributions.

If you are unsure, send a Dart to R&I. Especially if military with contributions on combat pay, that’s another can of worms. Not difficult, but additional steps required to keep the tax benefits.

And yes, so many jokes exist with these terms, but the IRS has accepted to backdoor terminology so it is what it is.