Does rental income to expense determine if the property can be depreciated? One of my 2 rentals have not been depreciated for years.

No. Rental property is depreciated no matter what.

Its common for rental property will operate at a loss each and every year the property is in service. Those losses that exceed the income are carried forward to the next year, where they can be deducted if the property has generated the income to deduct them from. But that doesn't happen every often - especially if there's a mortgage on the property.

Typically, when you add up the allowed deductions of property taxes, property insurance and mortgage interest, then include the depreciation you are required to take by law, the total will exceed the total rental income received for the year. Add to that other allowed deductions from rental income such as repairs, maintenance, advertising, etc., and you're practically guaranteed to have a loss.  But that does not negate the requirement to depreciate the property.

One of my 2 rentals have not been depreciated for years.

Precisely how many years? Have you checked the 4562 on that property to confirm beyond any doubt that it has not been depreciated? I ask, because the TTX program takes care of depreciation in the background and generally doesn't bother the user with those details. Of course, that's dependent upon the property having been set up correctly the first year it was placed in service.

If the property was placed in service before 2018 and you've confirmed no depreciation was taken, then you can not fix this yourself, as it will require professional help to get it right. While the TTX program does include the IRS Form 3115 that may be needed to fix this, that form is not simple by any stretch if you don't know what you're doing. Doing it wrong can cost you more in the long run.  Therefore, professional help would be required if the property was placed in service before 2018 and you have not been depreciating it.