Delete old iPhone data without messing up my new iPhone.

OK, so I’m finally ready after two weeks to let go of my old iPhone 12 Pro Max and trade it in. For some reason, I’ve been scared to reset it in fear I’ll lose photos/apps etc on my new iPhone.

I already downloaded everything to my new phone and backed it up so I think my data is safe.
Can someone give me step-by-step instructions on how to delete everything from my old phone (factory reset) without deleting any data from my iCloud or my new phone. I already turned off Find my iPhone on my old phone because I read you should do that.

There’s a message in my settings on my old phone that says “what’s next for this iPhone?” Then it says “get started” or “don’t erase phone”. Should I press get started or just factory reset it? Do I log out of iCloud first on my old phone? I’m very confused! Please someone help with easy steps. Thanks