Northwestern has rules that restrict undergrad transfers.
The deadline for transfer applications is March 15*. Note that Northwestern only considers transfer applications for fall-quarter enrollment. (The March 15 "deadline" was extended to April 10 unofficially, possibly because of the basketball portal)
Incoming transfers must have completed a full year of credits at their current university.
Incoming transfers must be able to attend NU for 6 quarters (two years) and complete at least 21 units.
Undergrad programs at Northwestern require 42-50 units for graduation, depending on the program.
Less than 15% of transfers are accepted. Minimum of B average on their college transcript.
Most transfers are admitted for their sophomore year.
My guess is that Jared Jones would not make it thru admissions at this point.
These rules eliminate many, possibly most, of the players in the basketball portal.
Graduate transfers are a separate category.