Free Trial doesn't work if licensed version used previously.
If a computer has ever had a licensed version of the product (like from a school, not a personal use), the free trial will not work FOR ANYONE EVER AGAIN ON THAT COMPUTER. Even if you sell your computer, the next person CANNOT USE A FREE TRIAL. Adobe does nothing to help.
This is intentional. A free trial period gets applied to the computer, and not a user, because it’d open a way to use free trial versions indefinitely, for each new user of the computer — creating users is free, while the software is not.
There are cheap educational licenses a school can purchase, if it want to teach their students: https://www.adobe.com/creativecloud/buy/students.html