Hello and welcome to JustAnswer.
Unfortunately, as an at-will employee you can be terminated at any time for any reason (as long as the reason isn't based on discrimination due to a protected characteristic, such as race, gender, national origin, or ethnicity) with or without prior notice.
Your employer, unfortunately, doesn't have to inform you of the reason for your termination, or provide you with information regarding the PIP, and it doesn't have to be based on your performance.
You should apply for unemployment benefits, since you are presumed to have been terminated through no fault of your own, which would entitle you to receive unemployment benefits.
Your employer could contest your benefits, but it would have the burden to demonstrate that you were actually terminated for cause and not through no fault of your own.
You can apply for unemployment benefits here: