I am writing the answer to reply to @ThomasLedan.

As mentioned I had to override the index.html:

• In a Swagger folder in my project, I added index.html as Embdedded Resource to my project, from Swashbuckle. I did this a while back and now they have split the index.html to multiple files, so adjustments are needed to include them in your project, or use the version I am still using.

  • Configured the plugins in index.html:

    ...
    configObject.layout = "StandaloneLayout";
    
    // My Custom Code
    
    configObject.plugins = [
        SwaggerUIBundle.plugins.DownloadUrl,
        AdvancedFilterPlugin
    ];
    
    // End My Custom Code
    
    // Parse and add interceptor functions
    var interceptors = JSON.parse('%(Interceptors)');
    ...
    

• Added /js/custom-swagger-ui-filter.js under wwwroot in my porject

// Originally from https://github.com/swagger-api/swagger-ui/issues/3876#issuecomment-650697211, refactored slightly
const AdvancedFilterPlugin = function (system) {
    return {
        fn: {
            opsFilter: function (taggedOps, phrase) {
                phrase = phrase.toLowerCase();
                var normalTaggedOps = JSON.parse(JSON.stringify(taggedOps));

                for (const [tagObj, value] of Object.entries(normalTaggedOps)) {
                    const operations = value.operations;
                    let i = operations.length;

                    while (i--) {
                        const operation = operations[i].operation;
                        const parameters = (operation.parameters || []).map(param => JSON.stringify(param)).join('').toLowerCase();
                        const responses = (operation.responses || {}).toString().toLowerCase();
                        const requestBody = (operation.requestBody || {}).toString().toLowerCase();

                        if (
                            operations[i].path.toLowerCase().includes(phrase) ||
                            (operation.summary && operation.summary.toLowerCase().includes(phrase)) ||
                            (operation.description && operation.description.toLowerCase().includes(phrase)) ||
                            parameters.includes(phrase) ||
                            responses.includes(phrase) ||
                            requestBody.includes(phrase)
                        ) {
                            // Do nothing
                        } else {
                            operations.splice(i, 1);
                        }
                    }

                    if (operations.length === 0) {
                        delete normalTaggedOps[tagObj];
                    } else {
                        normalTaggedOps[tagObj].operations = operations;
                    }
                }

                return system.Im.fromJS(normalTaggedOps);
            }
        }
    };
};

• in my Startup.cs or Program.cs:

...
app.UseSwaggerUI(c =>
{
    ...
    // custom filter as the default from EnableFilter() only filters on tags and is case sensitive
    c.EnableFilter();
    c.InjectJavascript("/js/custom-swagger-ui-filter.js");
    var assembly = GetType().Assembly;
    c.IndexStream = () => assembly.GetManifestResourceStream($"{assembly.GetName().Name}.Swagger.index.html");
});