Can I file electronically after correcting a 401K over contribution in other miscellaneous income (i.e. without a 1099R)?

[Rachel_W]

No.  Unfortunately, if you have an excess 401(K) Contribution, you won't be able to E-file your 2018 return.

There is currently an e-filing issue within TurboTax related to excess contributions so you will need to mail in your return.  You can check out this TurboTax FAQ for more information: Excess 401(k) Contribution Preventing E-filing.