RexSystem1 voteMerged from #685originally by @naelstrof on GitHub
This has since been fixed, there's a new article on the setup instructions here: https://docs.fluxer.app/operator/reverse-proxy/
Or perhaps, I didn't understand what reverse proxy meant when I initially followed the instructions.
Anyway, I took my completely stock installation and added the following to the .env:
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Comment by @naelstrof