Appears to be up to the school (link)

Here's an interesting article that covers the realities of the transfer portal.

Essentially, a school can only take 25 "initial counters" per year, up to 85 total scholarships. New recruits, juco transfers, and players from the transfer portal count against that 25/85. So unless one is a top-tier player, there may be a bit of a waiting game as all the things detailed in the original post shake out - coaches, commits, other higher priority transfers.

The article brings up the situation of a player entering the transfer portal, finding no takers, but then their original school needs to cut down to their 85 limit. An "easy" way to do that is to not extend another year of a scholarship offer to the player in the portal.

Click here for link at https://www.si.com/college/2019/02/18/transfer-portal-schola