It looks like one can enter the transfer portal if one has graduated from a 4 year institution and is going to another institution as a graduate student (and can obtain eligibility right away).
All others will require some type of waivers from NCAA.
The following article gives some additional information on the subject:
What are the NCAA Basketball transfer rules? A guide into the portal process
by Tristan Freeman 1 month ago Follow @hoopsnut351
The transfer portal has become more important than ever in NCAA Basketball. Here’s a look at how the process works and when to focus on it.
One of the most decisive topics in NCAA Basketball has been the transfer portal and whether or not it’s good for the game. But one thing is clear, it’s here to stay. Last season, around 1,500 players transferred at the D-I level alone, which is around four a team.
The rules have been all over the place from the NCAA, with many players transferring more than once, with most finding a way to get a waiver for various reasons that include being “ran off” from the previous school and not having a scholarship available, a coaching change, personal reasons and etc.
It’s been viewed as the “wild wild west” by pundits, coaches, and others, with calls being made to reign things in. And the NCAA, through various committees and boards, has come up with various changes to try and simplify the process for all.
New 60-day window
There’s a “window” for the time for players to officially enter the NCAA Basketball transfer portal for the different sports seasons, with winter athletes (basketball), having 60 days to enter after the conclusion of the regular-season/conference tournaments. So for the men and women, the deadline would be May 11th. Anyone who enters during this period will be able to become immediately eligible if it’s their first time transferring. Anyone who enters afterward will have to apply for a waiver, something that isn’t guaranteed by the NCAA. Grad students are exempt from this rule so veterans can move at any time.
Tougher requirements for multiple transfers
The NCAA has been trying to get out of the waiver business and has made it clear that anyone can transfer one-time without issue, as long as they’re academically eligible of course. But if they move a second time and aren’t a grad transfer candidate, they’ll have to get a waiver, which is going to have stricter requirements. Coach changing and personal reasons are likely to remain options but as the NCAA showed with West Virginia transfer Jose Perez, they’ll deny a player to get eligible if it’s not done in the offseason.