Some Feedback on SPA and Monoliths

For the opening episode of the Wazoo Web Bytes Podcast, I thought I'd start with an excellent comment on one of my YouTube videos which dealt with creating a React18 application within a Spring Boot server

Build Your Own Project List App with Spring Boot Server and React18 - YouTube

Questions that nearly everyone in web development faces during their career:
1. Is this a good way of building a web-app with Spring and React? 
2. How does it scale when you have a bigger web-app with many pages?
3. Why do we still need Thymeleaf?
4. Is this approach only viable for hobby projects or does it work well in enterprise apps as well?

Thanks for the feedback - other questions can be either submitted on any video or to erik@wazoowebbytes.com