Where do I enter the 1095-B in PROConnect Tax Online?

I do not think you need to enter 1095-B as the penalty for the lack of insurance has been eliminated.

Please see my signature to vote for my proposal for the good the user community, it should just take a few seconds. Thanks.

Federal penalty for individual mandate has been reduced to $0 as @puravidapto says.

Some states such as CA and MA, however, continue to assess penalties for failure to maintain MEC.  If your client is subject to penalties at the state level, you will still need to make the relevant entries from 1095-B.

The input for CA, for example, is under Credits > Premium Tax Credit (1095-A, 8962) > CA Premium Assistance Subsidy/Penalty and CA Form 3895 - Health Insurance Marketplace Statement.

Problem:  Penalty on CA 540 line 92 for tax year 2021.

Solution:  Input Return tab to Credits to Premium Tax Credit (1095A, 8962) to CA Premium Assistance Subsidy/Penalty.  There is a box labeled "Minimum Essential Coverage Not Indicated Elsewhere" enter 1 which indicates that entire household covered for entire year. 

Result:  Penalty amount should no longer be on CA Form 540 line 92 and the box is checked.