The standard ordering rules for the use of the credits on the form 1040 is that non refundable credits are used up first before refundable credits or ones that can be carried forward like the adoption & solar credits.
For 2021 the CTC is fully refundable so it moves down on the ordering list to allow the solar credit to move up in the pecking order. You cannot use the 2020 program to "what if" the 2021 return as it may not take this change of order into consideration. Most of the 2021 forms/instructions have not yet been written/posted yet.
