Philadelphia Flyers

As a result of his play, Foerster rose from the 41st ranking by the NHL Central Scouting Bureau in January to the 21st by April.^[8] He was invited to the 2020 CHL Top Prospects Game where he scored two goals and was named Player of the Game for Team White.^[9] He was eventually drafted 23rd overall by the Philadelphia Flyers in the 2020 NHL Entry Draft and signed an entry-level contract with the team on October 14, 2020.^[10]

With the hiatus of the OHL due to the ongoing pandemic, Foerster attended the Flyers training camp in preparation for the 2020–21 season. On January 13, 2021, he was re-assigned by the Flyers to AHL affiliate, the Lehigh Valley Phantoms training camp, in order to continue his development.^[11] In his first game with the Phantoms, on February 6, 2021, Foerster had an awkward collision with a Hershey Bears player that resulted in a broken tibia for Foerster.^[12] He was expected to miss 3-4 weeks.

On March 9, 2023, Foerster made his NHL debut with the Flyers against the Carolina Hurricanes, where he played on the ice for roughly fourteen minutes, blocked three shots by the Hurricanes, and had two shots himself against goalie Pyotr Kochetkov.^[13][14] He had his first assist on March 17 against the Buffalo Sabres,^[15] and on the following day, March 18, Foerster scored his first NHL goal against the Hurricanes' Frederik Andersen in the last five minutes of the second period.^[16][17] On March 26, after scoring three goals over a total of eight games played, Foerster was loaned back to the Flyers' AHL affiliate Phantoms.^[18]