Can I use TT Business to file my S-Corp taxes for the 2019 year, is it possible to import WHMCS invoices and such? If not, how does one import data into TT Business?

[VolvoGirl]

Yes you have to use Turbo Tax Business (not the same as Home&Business) to prepare a 1120 S corp.l

You can only import from QuickBooks.   Unlike many other TurboTax products, TurboTax Business does not support import from employers, payroll providers, brokerages, financial institutions, Quicken, Quicken Rental Property Manager, ItsDeductible, or Tax Exchange Format (.txf) files.

Here is the support article to import Quickbooks into Turbo Tax Business. TT Business will only import from Quickbooks CD/Download Software versions. TurboTax Business will not import from QuickBooks Online. Turbo Tax Business and QuickBooks must also be on the same computer.
https://ttlc.intuit.com/community/entering-importing/help/how-do-i-import-quickbooks-data-into-turbo...

[VolvoGirl]

By the way,  Turbo Tax Business is not available to do online or on a Mac. You can buy the Window's (Win 7 or newer) version here. And you can have both TT Business and TT Home & Business (or any personal version) installed on your computer at the same time.
https://turbotax.intuit.com/small-business-taxes