I went back to school in September of 2022 and attended university as a full time student through December. That's only 4 months, so do I get no deduction?

It depends on what you are trying to do on your own tax return or whether you are a dependent on your parent's tax return.

IRS definition for Student:

A full-time student is a student who is enrolled for the number of hours or courses that the school considers to be full-time attendance.

To qualify as a student, the person must be, during some part of each of any five calendar months of the year, be :

1. A full-time student at a school that has a regular teaching staff, course of study, and a regularly enrolled student body at the school, or
2. A student taking a full-time, on-farm training course given by a school described in (1), or by a state, county, or local government agency.

The five calendar months don't have to be consecutive.

There's more information you can use based on your specific details at this link: Tax Benefits for Education Information Center

Q. That's only 4 months, so do I get no deduction?

A.  No.

The 5 month rule does not affect YOUR eligibility for a tuition credit.  The 5 month rule only affects whether parents can claim a student as a dependent.  In fact, the most generous credit (The American Opportunity Credit) only requires that you be half time or more for some part of an academic term.  So, Sep to Dec, you qualify, if you were a degree candidate.   The lesser credit (Lifetime Learning Credit) is even less restrictive.