for 2021?  you mean your 2020 return. on the 1116 you were supposed to report the FTC carryover. then Turbotax would have based your allowable FTC bases on your 2020 FTC and the 2019 carryover.  the only way to fix this is to file an amended return for 2020. if you don't file an amended return you lose any extra FTC you would get for 2020 and can't claim any carryover in 2021.

I am still working on filing the 2020 return (due 10/15).

This year, unlike all years back to 1994, I am using the online version of TT due to computer problems (TT would never load on my Mac).

I have uploaded the 2019 return with the carry-over to TT.  But, the online version has not picked up the additional foreign tax credit.

This is not a question of tax law.  I just need to know how to input that credit.  How do I access the tax forms when using the online version.