How to structure and deploy server for multiple instances of the front apps with same business logic?

I'm a mobile/front-end developer and need help with the architecture on the back-end where I'm totally green. I'm building web and mobile front in Flutter that will communicate with the server written in GO. Based on the config file attached the Flutter front I will create few separate apps, but for every single app I need a separate instance of the back-end services or at least separate database.

My question is about what architecture I should use in terms of future scaling to lower the server maintenance costs while having the best performance. Correct me if I'm wrong because what I will write is the image of my understanding of the structure but based on what I wrote above - am I correct that I should use some load balancer with the business logic spread across Kubernetes instances and only have separate database for every single Flutter app? Or is there any other solution I'm unaware about? Any help or guides that will at least lead me to more knowledge I can learn would be much appreciated.