Such a rollover is not permitted. A distribution from the traditional account in one 401(k) is only permitted to be deposited into the traditional account in the other 401(k). Rollovers from the traditional account in one 401(k) are only permitted to be rolled over to the Roth account in the same 401(k) plan, a so-called In-plan Roth Rollover (IRR).
Because the such an out-of-plan taxable Roth rollover is not permitted, the Form 1099-R from the old 401(k) correctly shows a nontaxable direct rollover to the traditional account in the receiving 401(k).
Ignoring the fact that an out-of-plan taxable Roth rollover is not permitted, you might consider reporting it as if it was done in-plan. To do so you would have to enter a substitute Form 1099-R (Form 4852) with the taxable amount entered into box 2a accompanied by an explanation, but the explanation would likely tip the IRS off that you did an impermissible rollover.
The proper way to have done this would have been to either do an IRR in the old 401(k) (plan permitting) and then do a Roth 401(k)-to-Roth 401(k) rollover, do a rollover from the traditional account in the old plan to the traditional account in the new plan, followed by an IRR in the new plan. You could have also directed the old plan to do a taxable direct rollover to a Roth IRA, in which case the Form 1099-R from the old plan would have the taxable amount in box 2a.
This answer has been verified for accuracy by an Intuit expert employee
