The terms for congressman and the president end at slightly different times. The new congress that is elected is sworn in a couple weeks before the new president is. So it wouldn’t be whoever is currently elected deciding on presidential election certification, it’s whoever is elected next November that will be sitting at that point.
In 2021 for example, the new congress was sworn in on January 3rd, three days before the presidential election certification that was interrupted by an attempted coup on January 6th. Biden was sworn into office on January 20th.