Isaac played a significant role on Penn State's defense in 2022.
The linebacker totaled 72 tackles, 14 for a loss, and 13 sacks during the 2022 season.
Mulbah will enter the transfer portal will three years of eligibility remaining.
Kevin Wall and Liam Souliere have been an integral part of Penn State's success this season.
Shay Ciezki scored a career-high 21 points despite Penn State falling
82-72 to No. 14 Michigan.
The Nittany Lions remain at No. 5 for the second consecutive poll.