When I use the modeler (Pic. 1, Layer: "Gemeindegrenze/2500 m Radius" - yellow mark), the results are always shown in a value with 16 decimal points (Pic. 2) and It seems to be impossible to change it for 2 decimal points, while using the value expression (Pic. 2, red mark), even when I set up 2 decimal points (Pic. 2, orange mark) it is not working out. I found out that it does show me the number in 2 decimal points when I change the value expression to "area_perce", while keep the setup for 2 decimal points (orange mark). But in that way I can`t name the area in the map.
On the other hand (Pic. 1, Layer: "Gemeindegrenze" - blue mark), I also found out that when I skip the field calculator by using the modeler and calculate the "area_perce" (percentage of area) only by field calculator (by hand), it works perfectly with the value expression (Pic. 3, red mark) and does'nt even need to set up the number of decimal points (Pic. 3, orange mark). So I am pretty sure that the problem is somewhere in the field calculation from the modeler. At both layers I use a format template that I saved before, to have same settings and changing the result field type or result field length (Pic. 1, brown mark) did`nt change anything.