Rot on roof beam

Pictures are from inside my attic. This is the only portion that is affected, roughly 1.5 feet wide and 1 foot down. The immediate are around is soft but gets harder the further away. Additionally there is some new plywood sheets right above this part of the beam. There were solar panels installed before we bought the house but not sure if it is on this area.

Thoughts on what kind of repairs were made? Would this require the entire beam to be replaced? Is sistering this portion a possible fix?