Avoidance of MITM/in flight for electronic data is best done by not filing electronically (esp., given that if you use one of the tax prep packages, all your tax data flows through them unencrypted on its way to going to the IRS).
Print the forms to paper, sign them, stuff into an envelope, and file via the US Mail (sending certified return receipt if you like).
You should have already frozen your credit. If you haven't, follow these steps. It should take you about 15 minutes.
https://www.nerdwallet.com/article/finance/how-to-freeze-cre...