Current technology stack in your products?

Hey! I am a founder of a software testing school, and our main course is manual testing from scratch. We focus on 3-tier web applications testing with Linux, networks, REST, CSS, HTTP, sniffers, DevTools and of course, testing theory and methodologies and Agile approach, and on the internship test startup applications for free. And I want to ask you as startup founders, what technology stack do you use? What do you think, is our stack enough to cover current startups' needs? What makes sense to add or remove from the course?