That's crazy to me - tax returns for our micro-business and personal tax has been online since at least 2005.
Attaching statements — This program does not allow you to attach any documents to your return, except those available through the program. If you need to attach any such documents, you will have to print and mail in the return.
Especially with business returns, it's common to have to attach statements to certain forms, for example if you choose the de minimis election for equipment repairs that would otherwise have to be capitalized, or when the § 174 changes went into effect and everyone had to start amortizing software development expenses over multiple years. You can't do that on Free File Fillable Forms.
Why didn't you efile like a normal person? The only time you need to do it the hard way is if you are under 16 and filing for the first time.
Edit: In hindsight, I could have just waited until the start of 2025 to update my address in the HR system and gotten a single, normal W-2, but then I would be both violating the remote work rules (by not adding my new work location) and (probably) committing tax fraud.
