I lived in IL for most of 2023 and moved to MA at the end. It asks what the Non-MA Portion of FICA payments are. The W2 only shows it as one in W-2. Do I prorate?

Yes.  Allocating earned income (or withholding) is easy if you stopped working for an employer in one state and started working elsewhere after you moved.  All you need to do is look at your W-2 or 1099-MISC. Allocate the income from your former job to your former state and your income from the new job to your new state.

What if you continue working at the same job while living in 2 different states? Some companies will send you a W-2 with the state totals listed, others will send you two separate W-2’s for each state. If not or they didn't change the withholding to the second state, then you’ll have to estimate how much income you earned as a resident of one state versus the other. Here are a few ways to do that.   That link has examples.