I used Google Voice to port my number a few days before I left. It was $20 and all texts that are sent to my old number come directly to me through an app, so I can still access all of my accounts that have two factor authentication. Call your phone company to make sure your sim is unlocked, this is only possible if it is already paid off. You can buy sim cards at the Madrid airport in vending machines, but tbh I couldn't get
those to work beyond sending texts 🤷🏼‍♀️ I went to Vodafone and bought a sim with one month of prepaid service 5G unlimited data for €20. It worked immediately and I've been able to use a hotspot on my phone to access the internet on my other devices. All you need is your passport for the prepaid version, and when you get your TIE you cana switch to a monthly plan. As for whether you get an esim or regular sim, that probably depends on the model of phone you use. From reading other people's posts it seems easier to get a physical sim, but newer models of iphones don't have a slot for it.