One easy way I sometimes validate software architectural solutions I am working on is through 𝗽𝗿𝗼𝘁𝗼𝘁𝘆𝗽𝗶𝗻𝗴.
According to wikipedia, a prototype is an early sample, model, or release of a product built to test a concept or process. In my case it validates that the solution fits, and must do it fast.
To make thinks easier I leverage as much as I can on existing tools, libraries or platforms and only build what is needed to validate the solution or proof a concept.
To substitute backend services doing simple CRUD operations I use 𝗵𝗲𝗮𝗱𝗹𝗲𝘀𝘀 𝗰𝗼𝗻𝘁𝗲𝗻𝘁 𝗺𝗮𝗻𝗮𝗴𝗲𝗺𝗲𝗻𝘁 𝘀𝘆𝘀𝘁𝗲𝗺𝘀. What a headless CMS does is making content available through an API, allowing me to use it as a content repository.
Headless CMS come in many different forms and implementations. Some have OAuth2 support, some have GraphQL support, some support certain databases.
Of course, headless content management systems are not just useful for prototyping, some are mature products that can successfully be used in production systems.
To decide upon which headless CMS to use based on your requirements, the https://cms-comparison.io/ website is very useful.