New iPhone SE not pairing with 2018 Lexus 350RX in Bluetooth, it just spins

Have you gone into the Lexus to start the pairing process? With most cars the car system looks for the Phone, not the other way around. See this link, but also check the user manual for your Lexus to see how it pairs on the Lexus side --> How to connect your iPhone, iPad, or iPod touch to your car - Apple Support

Have you told your Lexus to forget you previous phone? Also in Settings > General > About > Name, have you renamed your new phone, as sometimes car are looking for the old phone if they share the same name.