Many have eSIM...but not all. There are pros and cons to each. The question here is that to obtain a SIM from a carrier will you have to go through KYC? I believe the answer is yes, but I frankly don't know for sure...

The SIM (and the IMSI) identify the user of the phone (i.e. your phone call and text destination). Assuming that a "burner" phone has a SIM that is not attached to your identiry? If so, then a phone with a non-KYC SIM running #grapheneOS would seem to be an optimal combination.

But (for most?) that would entail getting a new phone number (and I think that's likely unpalatable for many). 

#asknostr