You are correct, Form 3520 is a complex form. Though TurboTax can handle many complicated forms and calculations, Form 3520, Annual Return To Report Transactions With Foreign Trusts and Receipt of Certain Foreign Gifts is not supported at this time.
The form should be filed separately from your tax return. Here are the IRS links:
IRS Form 3520 - https://www.irs.gov/pub/irs-pdf/f3520.pdf
IRS Form 3520 instructions - https://www.irs.gov/pub/irs-pdf/i3520.pdf
