I have all of it.

libx264 is linked in gst-plugins-ugly.

I found some more information here:

https://gstreamer.freedesktop.org/documentation/tutorials/basic/gstreamer-tools.html
https://stackoverflow.com/questions/17096139/your-gstreamer-installation-is-missing-a-plug-in-gsturidecodebin

Then I tried this:

--8<---------------cut here---------------start------------->8---
> gst-launch-1.0 -v uridecodebin uri=https://old.reddit.com/r/funny/comments/a53e07/finally_redone_correctly/
Setting pipeline to PAUSED ...
Pipeline is PREROLLING ...
/GstPipeline:pipeline0/GstURIDecodeBin:uridecodebin0: source = "\(GstCurlHttpSrc\)\ source"
ERROR: from element /GstPipeline:pipeline0/GstURIDecodeBin:uridecodebin0/GstCurlHttpSrc:source: Internal data stream error.
Additional debug info:
gstbasesrc.c(3055): gst_base_src_loop (): /GstPipeline:pipeline0/GstURIDecodeBin:uridecodebin0/GstCurlHttpSrc:source:
streaming stopped, reason error (-5)
ERROR: pipeline doesn't want to preroll.
Setting pipeline to NULL ...
Freeing pipeline ...
--8<---------------cut here---------------end--------------->8---

Which is precisely what your patch is trying to fix.  Hmm...

-- 
Pierre Neidhardt
https://ambrevar.xyz/