Customised version of the back case by Graeme647 on the one from ggiavelli which reduces grids making them more strong and use a support for the narrower back hole for LCD flat cable.

There is the bottom hole for a separate bung to block the speaker so you can decide whether to install it or no (See ggiaveli thing).

NOTE:
you have to use 2 slightly longer screws and 2 even longer screws to connect it.

I bought a package of M3 x 30 and cut two of them at 10mm and the other two at 16/17 mm

Ender 3

No

Yes

0.2

20

Use just one support for the bridged part - just 10% support infill, 70°, ZigZag pattern

Adjustments made in Tinkercad and Blender.
Used Netfabb to check the mesh