Nordic Thingy:91™ is equipped with a nano-Subscriber Identity Module (SIM) (4FF) card slot. As of Nordic Thingy:91 v1.4.0 it is also equipped with a footprint for an MFF2 SIM card.
Figure 1. SIM card schematic for Nordic Thingy:91 v1.0.0
Figure 2. SIM card schematic for Nordic Thingy:91 v1.4.0
Switching between the two types is controlled by the presence of a 4FF SIM card.