Can I manually enter on my 2020 return a carryover amount from 2019 for disallowed section 179 property on line 13 of Form 4562 Depreciation?

No. Enter any Section 179 carryover from last year on the Smart Worksheet of each activity that has a carryover. Enter carryovers of K-1 pass-through deductions on the K-1 Additional Information 1 forms. 

@ErnieS0 

The poster is using the ONLINE program which doesn't have the FORMS mode so the answer is useless and the screenshot is impossible to read ... you need to use the attachment function in this forum instead of cut & paste.   

@jojo34 As incredibly awesome @Critter-3 pointed out, the solution I posted is not helpful if you are using TurboTax Online.

If your Section 179 carryforward is from Self-employment income and expenses, go to Carryovers, limitations, at risk information, etc. and select I had unused section 179 expenses carrying over from 2019.