Can you explain what you consider a "Custom" component?
There is often a lack of understanding regarding what gets rendered in the AEM SPA Editor. My recommendation is to carefully read this article that delves into how the AEM SPA Editor works: https://experienceleague.adobe.com/docs/experience-manager-65/developing/spas/spa-overview.html?lang=en.
This article provides clear details on how components work and render within the SPA Editor. That being said, if your "custom" components do not meet these conditions, it won't render. That was clearly the issue in the thread you have pointed out.
I have used many custom components in the SPA Editor, and they work well when following the guidelines provided in the documentation, as outlined in this link: https://experienceleague.adobe.com/docs/experience-manager-learn/getting-started-with-aem-headless/spa-editor/react/custom-component.html?lang=en.
Hope this helps.