Need help with software design and architecture planning

Hi everyone! I’m a junior developer working alone without any senior guidance at my workplace. I create business applications for internal use and keep running into issues when trying to plan out the technical design and structure of my projects.

I really need to learn how to properly design software systems, create database schemas, and map out the overall architecture before I start coding. I’m looking for good learning materials that cover topics like creating class diagrams, system design patterns, and UML modeling.

Most online courses I’ve found focus more on project management stuff like scheduling and agile practices rather than the technical design aspects. Does anyone know of quality resources or training programs that teach software architecture fundamentals?

For context, I mainly work with Blazor applications that handle things like file processing, user authentication, database operations, third-party integrations, and cloud services. The business needs vary quite a bit so I need flexible design approaches.