I think even first year can use the transfer portal. There was the Ohio state recruit who gave up his senior year in high school to start early at OSU and I think he took summer or fall classes but then wanted to leave before he even played a down and used the transfer portal.
It may be that he never signed a NLI so maybe he didn’t have to use the portal. I don’t think he was eligible for the NLI as a hs junior/quasi senior.
With the new NIL rule (one of the reasons he left his high school, the other was to avoid injury) many student may not even care about the NLI/scholarships anymore. Some are bringing in more than the scholarship is worth. I think this kid was making a million as a 17 year old, all kinds of deals for cars and advertisements.