"Why do you need an EFIN?"
Because the IRS requires it for those who electronically file.
"What are the EFIN requirements?
Effective in the tax year 2011, federal legislation mandates anyone filing more than 10 returns must electronically file. Before you can electronically file tax returns, you must apply to become an Authorized e-File Provider with the IRS and obtain an EFIN."
"To use TaxConnect you need to already have an EFIN."
Nope.
https://proconnect.intuit.com/proseries/efin-ptin/
"In order to e-file a return, you must have an EFIN number. Both e-file and paper filing are available."
https://proconnect.intuit.com/tax-online/faqs/
And
https://www.irs.gov/e-file-providers/faqs-about-electronic-filing-identification-numbers-efin
"I have been using TurboTax for many years and was expecting the same kind of professional user interface. My mistake."
TT is DIY; not for professionals who are preparing returns for others. TT can be used by Forms or by Interview; and you can jump from one to the other.
You have to pick your lane, then use the tool that applies.
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"Level Up" is a gaming function, not a real life function.