In CMS 12.22.8 and onwards (at the time of writing this post 12.22.8 and 12.23.0) the client resources (e.g., custom styles for UI) from root module (i.e., defined in module.config in root of the project) are no longer loaded by CMS UI.
The resource is requested by CMS UI, but 404 is returned.

Steps to reproduce:

1) Create empty alloy project with dotnet new epi-alloy-mvc --name AlloyTest
The default version of CMS in template is 12.18.0 at the time of writing
2) Create root module.config with following content

<?xml version="1.0" encoding="utf-8"?>
<module>
    <assemblies>
        <add assembly="AlloyTest" />
    </assemblies>
    <clientResources>
        <add name="epi-cms.widgets.base" path="Styles/Styles.css" resourceType="Style"/>
    </clientResources>
</module>

3) Create ClientResources/Styles/Styles.css with example content

.epi-form-container__section__label-container {
    font-size: 1.2em;
}

4) Run the solution - the custom style is loaded from https://localhost:5000/ClientResources/Styles/Styles.css in CMS UI
5) [Optional] Upgrade CMS to 12.22.7 - the custom style will still be loaded
6) Upgrade CMS to 12.22.8 or 12.23.0
7) Run the solution - the custom style will no longer be loaded, although CMS UI will try to load it, but the URL will return 404



I suppose this is an unintended side effect of mitigation of vulnerability found in 12.X - https://world.optimizely.com/blogs/Magnus-Rahl/Dates/2023/9/vulnerability-in-cms-12-shell-module-configuration/ 
However linked blog post didn't mention any required changes in module.config to still run custom styles, and any changes clientResourceRelativePath didn't make any difference.
If someone knows solution or how to workaround this, I would be grateful for hints :)