How many passes for the same render? 2048 is very noisy. I put 50 000 to have something worst than your pic. Did you use a denoiser?

All I can see is you simply used the built-in glass shader.

As far as I undertand, it's not about emitting shadows, but receiving them? I see you have 2 different planes and one placeholder, which do the trick. I assume they all are needed? Is it just the right combination of materials, or is there something noteworthy in the settings as well? I use version 4.3.