Sony RX100 IV has a 20.0MP 1" (13.2 x 8.8 mm ) sized BSI-CMOS sensor and features Bionz X processor. On the other hand, Fujifilm X100T has a 16.0MP APS-C (23.6 x 15.8 mm ) sized CMOS X-TRANS II sensor and features EXR Processor II processor.
Below you can see the RX100 IV and X100T sensor size comparison.
As seen above, Fujifilm X100T has a 3.2x Larger sensor area than Sony RX100 IV. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.