Sitecore SxA Composite Layout not adding custom css and js

I don't see any additional pieces of information from your side (as it was suggested in the comments) so I will write what I think you might be missing.

You wrote that you have a custom AccordionMvcLayout.cshtml. If you will take a look inside of that file, you will notice that on the top there is something like:

@{
    Layout = Sitecore.Configuration.Settings.GetSetting("XA.Feature.Composites.CompositeComponentLayoutPath", "Composite Component Layout.cshtml");
    ViewBag.Title = "Edit accordion item";
}

This view is using its own layout which is most cases (if not changed) is Composite Component Layout.cshtml. Go there and you will find the following lines in that file:

@{
    AssetLinks assetLinks = AssetLinksGenerator.GenerateLinks(new CompositeThemesProvider());
}

...

@foreach (string style in assetLinks.Styles)
{
    @Html.Raw(style)
}

...

@{
    foreach (string script in assetLinks.Scripts)
    {
        @Html.Raw(script)
    }
    ...
}

This code is responsible for rendering CSS and JS link. So double check if you custom layout have Layout = Sitecore.Configuration.Settings.GetSetting("XA.Feature.Composites.CompositeComponentLayoutPath", "Composite Component Layout.cshtml"); just like the original one.