As you might guess from the long reply in this thread, because this is a new deduction, there are some aspects not fully sorted out. Whether the rental activity of a person with one or two homes is QBI can be disputed. There are some "safe harbor" provisions, but you might choose to identify your rental as either QBI or not without using those "safe harbor" provisions.
Of course, if you don't take the QBI deduction, you won't have any problem as the IRS never disputes extra taxes, but generally you are safe if it is a business activity.
When is it not a business activity? For one, when you don't make money. If you don't usually make money (e.g. from rents) then you are assumed not to be doing it as a business. But then you wouldn't need a QBI, since it only applies to your profit.
There may be other situations. Investments are generally not managed by the investors, unlike businesses. So if you own shares in an investment, and just get a statement every year showing whether it made money and what taxes you owe, you may not be running your own business. On the other hand, if you're choosing tenants, collecting rents, and contracting for services (like installing new carpet, et al) then you likely are running a business, even if you think of it as an "investment property." That may just mean it's not your second home. This may be true even if you spend less than half your time or 750 hours a year managing the property or properties.
Remember that TT (Turbo) only approximates the description of blanks on the tax forms from the IRS it is trying to fill out. Ultimately we are each responsible for how we fill out the tax forms, regardless of how TT phrases the questions in "interview" mode. So if you have doubt about the questions, answer them the way you think makes sense, then check the forms to be sure you agree with how they're filled out! TT is still not responsible for how we fill out the forms in the eyes of the IRS, we are.
While TT sometimes references IRS instructions, the IRS publishes its own instructions and forms, and these are the basis for how we pay tax, not TT's best efforts to bridge the gap.
