I have now switched to the Dart Sass compression option, which fixes it:
{{ $opts := dict
"transpiler" "dartsass"
"outputStyle" "compressed" // ← Added
"targetPath" (printf "css/style.%x.css" now.Unix)
}}
{{ with resources.Get "scss/style.scss" | toCSS $opts }} // Removed
<link rel="stylesheet" href="{{ .RelPermalink }}">
{{ end }}
I think I had the trailing minify step from past projects where I concatenated SCSS + CSS. There are other solutions for that I reckon, like minifying separately before concatenation (or just minifying redundantly).