[KevinH]

Okay, so my problem was how I forced it to use Hyphenopoly by adding my own config info, made it ignore the path you had internally set.

So I changed the _loader.js to enable "FORCEHYPENOPOLY", in its internal config and I can see from the Inspector and the javascipt error console that the wasm file is being found and loaded and that Hyphenopoly.js is being loaded as a blob.

All as expected, but how can I tell if it is actually working or not given hypehnation is built in (at least on macOS)?

So this is an improvement but it requires the following change (which I just pushed to Sigil master):

diff --git a/src/main.cpp b/src/main.cpp
index ee33f91ce..26290878c 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -372,10 +372,11 @@ int main(int argc, char *argv[])
 
     // register the our own url scheme (this is required since Qt 5.12)
     QWebEngineUrlScheme sigilScheme("sigil");
-    sigilScheme.setFlags(QWebEngineUrlScheme::SecureScheme |
-                         QWebEngineUrlScheme::LocalScheme |
-                         QWebEngineUrlScheme::LocalAccessAllowed |
-                         QWebEngineUrlScheme::ContentSecurityPolicyIgnored);
+    sigilScheme.setFlags( QWebEngineUrlScheme::SecureScheme |
+                          QWebEngineUrlScheme::LocalScheme |
+                          QWebEngineUrlScheme::LocalAccessAllowed |
+                          QWebEngineUrlScheme::ContentSecurityPolicyIgnored |
+                          QWebEngineUrlScheme::FetchApiAllowed  );
     // sigilScheme.setSyntax(QWebEngineUrlScheme::Syntax::Host);
     sigilScheme.setSyntax(QWebEngineUrlScheme::Syntax::Path);
     QWebEngineUrlScheme::registerScheme(sigilScheme);

which tells Sigil to allow our "sigil:" schmemehandler to use the fetch api.

Update:

The problem is QWebEngineUrlScheme::FetchApiAllowed is only allowed in Qt 6.6.0 and later.

I will have to ifdef that to Qt version.