My renter was unemployed and ill the entire year of 2019 and did not pay rent. Can I deduct the rent as a loss?

[Critter]

NO.  You cannot deduct income you never received ... but you do get to deduct all the expenses you incurred during the year ... along with the depreciation. 

[JamesG1]

Whether you can deduct the unpaid rent as a loss depends on your method of accounting for your 1040 Schedule E rental real estate activity:

• If you are an accrual basis taxpayer, then you would record this on the Other expense line and just title it Bad debt.
• If you are a cash basis taxpayer, then there is no bad debt because you have not previously recorded the income. income.

See also here.