This is what I did:
.NET Core (because I knew .NET), Razor pages. Plenty of recipes on the next for integrating with 3rd party auth.
AWS because I had credits.
Docker for deployment to ECS (initially started on Elastic Beanstalk though).
I do use some AWS specific services (DynamoDB,Lambda,S3,AuroraDB) but as a single person startup I wanted to avoid as much maintenance / backup stuff as I could.
GitHub for source code control. Some use of GitHub actions.
VSCode for editing/debugging. JetBrains Rider is really nice though. Android Studio for the app.
Dev workstation: Linux or WSL2. Moved all the CI/CD stuff to makefiles or used GitHub actions. I found it more productive to ignore all the wizards and whatnot and learned the CLI for AWS and .NET. Android Studio is much nicer on Debian than it is in Windows.
For security: Tailscale.
For developement and testing: bought my own S/H server.