Do you force ssl in Discourse settings?
Can you run magick --version as discourse user? For me the output is:
Version: ImageMagick 7.1.1-45 Q16-HDRI x86_64 3cbce5696:20250308 https://imagemagick.org
Copyright: (C) 1999 ImageMagick Studio LLC
License: ImageMagick | License
Features: Cipher DPC HDRI Modules OpenMP(4.5)
Delegates (built-in): bzlib cairo djvu fftw fontconfig freetype gslib gvc heic jbig jng jp2 jpeg jxl lcms lqr ltdl lzma openexr pangocairo png ps raqm raw rsvg tiff webp wmf x xml zip zlib zstd
Compiler: gcc (13.3)