There have been a number of players (in both football and basketball) who have continued to play for their teams after entering the portal. Essentially they are saying that they will transfer but they are still a member of the team. Remember, under the temporary 5th year allowance, there is no obligation for schools to fund that 5th year with a scholarship. The Ivy League said at the outset that they would not do that. That's why you see a lot of Ivy players in the transfer portal.
If a player knows that he won't receive a scholarship for that additional year, I don't see anything wrong with him entering the portal while he's continues to play for his team for the remainder of the season.