Any major tech stack will work fine. I assume “real time alerts” will need an integration with a 3rd-party notification provider (email, sms, etc) and the bulk of your business logic will be defined with whoever is providing your share price API.

So, tech doesn’t really matter, pick something simple and mainstream so you can get help as needed.

Ruby/Rails, Python/Django, Nodejs, Java, whatever. Postgres for a database.

You likely won’t need any exotic cool tech, novel databases etc.