How many sims can an iPhone have?

It can have 2 sim cards active at any one time. 1 physical sim card and 1 eSim.

And it can have 8 eSims configured, but not active.

click here ➜ About eSIM on iPhone - Apple Support

Here’s another article info on the subject.

While it DOES contain quite a bit of overlap w/ link in 1st reply, it also contains some additional info.

Using Dual SIM with an eSIM - Apple Support