The coach should hopefully understand that this situation is different. If they don’t then that seems pretty messed up as the athlete isn’t reneging on any commitment to the team during the season but is looking for school after.
My advice: have the athlete talk to the coach to see if the coach understands the nuance between the situations.
On the transfer portal an athlete can be coded as a grad transfer (a little graduate hat pops up) so coaches know the athlete is looking for grad school. The athlete can also indicate they don’t want to be contacted by other schools if they have a list of schools they want to talk to and don’t want random schools to reach out.
Bottom line is if the athlete wants to compete during their grad year they have to be on the portal, the sooner the better. If the coach doesn’t understand that then maybe the administration at that school will and will override the coach. I’m not usually for that but if the coach won’t allow it for a grad transfer that coach needs to reevaluate their rule.