Yes, Qt is a perfect choice for many developers, but there are also some developers who can't fully master C++. For example, I'm not smart enough to learn C++ and can only use C. Fortunately, there are some C language UI libraries available.
AWS using ECS/ECR to start containers in an auto scaling group and behind a load balancer for an API layer. Similar setup for background workers. Starting with 2 instances for API, more for redundancy and ramping up as load increases. One or two smaller EC2 instance can handle the UI (SPA application). Database on RDS when funds increased, but initially just on another EC2 instance to save costs. Opting for running own services on EC2 was cheaper than managed.
For the backend, it's written in Rust using a few key crates: axum for the api, bgpkit-parser for parsing the MRT data, and reqwest for fetching data at boot.
The site is hosted on Neptune Networks, another side project of mine for people to learn and experiment with BGP.