downgrade ghostscript to get convert etc working

[Emanuel Berg <moasenwood@zoho.eu>]

It seems convert doesn't work on Debian Buster, I get an error for
this command

  convert -composite $bg $fg -gravity center comp.png
  
namely this message: "convert-im6.q16: no images defined `comp.png'
@ error/convert.c/ConvertImageCommand/3258."

I heard the solution is downgrade ghostscript but
'aptitude versions' only shows one version, 9.27 (or
9.27~dfsg-2+deb10u3).

Do I need to add additional sources or how do
I downgrade to a version that doesn't have the bug?

TIA

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