Fujifilm X-T1 has a 16.0MP APS-C (23.6 x 15.6 mm ) sized CMOS X-TRANS II sensor and features EXR Processor II processor. On the other hand, Canon R6 has a 20.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Digic X processor.
One other difference between these two cameras that is worth mentioning is that Canon R6's sensor doesn't have an anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the X-T1 and R6 sensor size comparison.
As seen above, Canon R6 has a 2.3x Larger sensor area than Fujifilm X-T1. 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.