Hello Sascha,

the fillet fails. Ok, but it creates a surface you can use for a trim. So create all the failing fillets. Then trim the body with the surfaces created by the fillet function and delete the useless fragments. Then trim each of the fillet surfaces with the rest body - it's now a joined surface. Remove while trimming the useless surface fragment. After that, join the surfaces with the joined surface to a solid.







Or you can use here a second solid and use Boolean - intersect.

Create a rectangle and enable round corners. From one to the opposite vertex of your geometry. Choose a radius. After That create a extrusion. Now make a intersection of both solids.


Have a nice day
Karsten