This is a bug.
I signed up for the free Stock trial with 10 images, but I am unable download any images from the trial.
When I click on the button next to it that says, "Download free with trial."
This directs me to a series of windows. The first one directs me to select a monthly or annual subscription, even though I've already done that and I'm signed in.
The next popup says, "Good news, looks like you already have a plan."
There was a similar bug which was recently mitigated - https://community.adobe.com/t5/stock-bugs/can-t-download-stock-images-with-free-trial/idi-p/14038221
Thanks!