Bevel and Subdivision surface issue

Question

I wanted to bevel a corner of a rounded mesh but it glitches out.

This is the starter mesh:

and this is the beveled mesh:

I want to bevel the mesh a lot more but if I do this it looks like this:

With subdivision surface it looks like this:

I checked for duplicate vertices with "Merge by Distance" in edit mode but this didn't help me.
Here is my blend file

Answer 1

The problem is, that you have a lot of long, stretched out faces on the top of the model. Not something you want to have, in general. Consequently, some edges of the top surface run parallel and very close to the (bevel)edge. When you add the bevel, you'll end up with overlapping geometry.

You should try to redo the geometry at the top and generate a more grid-like result. You can achieve this by deleting all top faces in edit mode. Then, select the edge and press F to create a face. - Then press I to inset the face. Make sure to inset far enough to leave space for the bevel. (While insetting is active, you can toggle the Boundary option by pressing B. This prevents the extra face at the boundary of the mirror modifier.) Inset once more for good measure.

This is what it should look like:

Then, (IMPORTANT) - Apply the scale of the model, or the bevel will look off. In object mode, press CTRL + A -> Scale.

Edit: In order to have the Subdivision Modifier behave well, you'll want to add another holding edge on the side part. In edit mode, press CTRL + R to get something like this: