Thats what I thought as well - one physical SIM and one eSIM, but this user in the comments section on egadget seems to have 3 total providers , two physical and one eSIM.
T-Mobile has rolled out an update for the Samsung Galaxy Note 20 Ultra that adds eSIM support to the phone, allowing you to use your number without having to slot in a physical SIM.
www.engadget.com
"The dual sim tray I purchased works fine on my Note 20 Ultra with the latest T-Mobile Firmware, I have my eSim installed, and 2 other sims installed one from AT&T that is just internet(from a hot spot as the sim2 and a verizon sim from work) so I have 3 service providers set on one phone. and all 3 sims visible and different set of notifications for all 3."
If it helps, my Note 20U is a TMO version but purchased through Samsung Insights program.