Leica SL2 has a 47.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Maestro III processor. On the other hand, Leica M Typ 240 has a 24.0MP Full frame (36 x 24 mm ) sized CMOS sensor .
Leica SL2's sensor provides 23MP more than Leica M Typ 240's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Another difference between these two cameras is that Leica SL2's sensor lacks 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 SL2 and M Typ 240 sensor size comparison.
Leica SL2 and Leica M Typ 240 have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Leica M Typ 240 has 97% larger pixel area (36.50µm2 vs 18.49µm2) compared to Leica SL2, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.