Can you explain how the Father "Dropped out"?

Was there some kind of legal document transferring his ownership % to the son? (Gift, Sale, etc.) or just quit working in the business.

If so when was it dated. Unless the transfer happened in 2020, the Father would (Probably ) been a partner for a portion of 2021, and may need to receive a K-1 for his ownership percentage for the portion of the year he was an owner.

If there was a transfer, and it happened during 2021, the Partnership may have terminated on that date, and become a Proprietorship at that date.

If any on those happened, I am not sure the way you are planning to handle it would be correct.