You don't. The loss gets carried over to future years when there may be basis.

Form 7203 may be required for 2021, though.

Thank you, that is what I thought, but in future year where there is basis, hw do you report the K-1 loss?

I don't use ProSeries, but way back when I had to do this in Lacerte,

I would enter it as a separate K-1 line item called prior year loss allowed or something like that.

Lacerte does these calculations for us now.

In ProSeries on the K1 line showing the loss, I use the supporting statement for that line showing basis, and loss. That way I don't have to override. I then keep the clients basis in his/her file