but, the carve solver was dropped since 2.8. Does anyone have any workaround or technique to achieve this in blender > 2.8?(except for the remeshing in blender sculpt mode, which is destructive as well as requires too much density to cover the details)
Yes, Cikitta Tjok is right. You can use the Boolean Modifier and select Union.
If you like, in the viewport you can go to Object -> Apply -> Visual Geometry to Mesh.
This way you can apply the modifier on the mesh and "bake" it. This step makes both sides of the mesh editable for weight painting, for example.