If I leave Spain and hand in my residency before 183 days into 2024, will I have any tax liability to Spain beyond paying my 2023 return?

As you are already tax resident I don't think the concept of 183 days in the year still applies.

My understanding is that you will still have to submit a return for 2024 but with less than 50% of the normal income for the year your tax bill should be minimal if anything at all.

Note that handing in your residency (to whom and where?) is one thing, detaching yourself from the Spanish tax system is something else but I believe there is a procedure for doing it.

Thanks for your reply.
That sounds a sensible system.
One Gestor has told us that for up to two years after our exit, should we sell any assets then Spain would tax us.
I can’t find anything online that would support this. We are not eligible for exit tax as we’ve only been resident for three years.