How much in deductions must I have to file single long form?

Since the standard deduction for a single person is $12,950, you would need more than that in order for itemizing to be beneficial. In addition, if you are blind or over age 65, you get an additional $1,750.

Remember that medical deductions, mortgage interest and SALT deductions all have limitations. 

I think you are talking about itemizing your deductions. You will benefit from itemizing if you have itemizable expenses over the standard deduction amount.

2022 STANDARD DEDUCTION AMOUNTS  

SINGLE $12,950  (65 or older + $1750) 

MARRIED FILING SEPARATELY $12,950  (65 or older + $1750) 

MARRIED FILING JOINTLY $25,900  (65 or older + $1400 per spouse) 

HEAD OF HOUSEHOLD  $19,400  (65 or older +$1750) 

Legally Blind + $1750 

There is no short form or long form. All tax returns are filed on the same Form 1040. The short form was eliminated in 2018.

You can file a tax return no matter how much or how little you have in deductions. If your total itemized deductions are less than your standard deduction you will use the standard deduction. If your total itemized deductions are more than your standard deduction you will use the itemized deductions. The itemized deductions will be shown on Schedule A included with your Form 1040 tax return.

If you are single, under 65, not blind, and not a dependent, your standard deduction for 2022 is $12,950.