I got my s20fe and bought it because is supposed to come with esim after getting it and talking to support i realized it is not enabled, maybe in the future but now I see my self returning this phone because it is unknown when the update will be sent to use esim.
All the S20 line up in Canada comes with esim as well as a slot for a regular nano sim...
By doing this you can activate the esim with your carrier here in Canada and use the nano slim tray for a 2nd sim card ie an out of country one in my case a uk sim so in effect you have 2 phone numbers assigned to your phone.
I Have contacted my carrier which is Bell and they confirmed what said above. If you wish to use the esim you have to tell your carrier so they activate the esim in the phone with your number and this leaves the tray empty for a 2nd sim card..
Bell and Virgin support esim not sure of other carriers.. just been in contact with Roger's they also support esim...
Koodo and Telus support esim. I am currently with Koodo and I have an esim voucher on hand.
I am very much hoping the s20 supports esim. It seems no one knows for sure if the s20 lineup will come with esim capability enabled (for NA markets).