6 YOE as an application developer - What should I learn to get to the next level?

There's an assumption baked in your question that reaching the next level requires mastering technology or learning a new domain. This is usually not true.

Here's the algorithm for getting promoted:

• Ask your manager how you can help the team
• Do the work to help your team
• [Now you have built some trust] Ask your manager what work you can do which will demonstrate your ability to work at the next level.
• Do the work to help your team (again)
• Ask for the promotion

If you've decided to leave ServiceNow, I'd focus on interview prep, but you shouldn't expect to get a higher level from job hopping.

Working on internal tech is definitely bad for your career - A lot of it doesn't carry over to other roles, especially during the interview phase. As you seemed to have figured out already, I recommend switching out of this space.

When you're in a situation like this, you have 3 options. Here they are in order of the ones I like the most to the least:

1. Find more fulfilling work on the job - You can do this by creating scope and/or asking your manager for different types of projects. For the creating scope part, here's a resource to help: [Taro Top 10] How To Create Scope As An Engineer
2. Build side projects - You don't need a business to get experience building cool stuff: The beauty of software is that anybody, anywhere can code up something incredible that adds value to the world. Here's our playlist for side projects: [Taro Top 10] Building Impressive Side Projects
3. Switch to a different team - This can either through an internal team switch (preferred as interviewing sucks and the job market is horrible) or changing companies. If you decide to take this route, I highly recommend watching this: [Masterclass] How To Choose A Good Company And Team As A Software Engineer

If you have more time after all of that, check out this other discussion as well: "How do I get better at building Large scale systems without working directly on such projects?"

What should I keep doing to reach to next level? Is this experience good or should I look for more Java/Spring or Python-related work? Or should I start learning AI/ML Stuff???

Getting to the next level is more about behavior, not raw knowledge. This is especially true that you're already a senior engineer where the next level is staff. Check out this playlist to learn more: [Taro Top 10] Senior Engineer To Staff Engineer (L5 To L6)

If you do want to pivot into a new tech stack, Java/Spring, Python, and AI/ML are all broad domains with significant staying power in the market. Figure out what you like and go from there. Do not just go into AI/ML as it's trendy. Here's a great thread about that: "Is it worth transitioning to become a Machine Learning Engineer?"

My interviews are mostly based on DSA/System Design/LLD topics only. Mostly my interview knowledge is not relevant to work. Suggestions appreciated on what I can do to grow.

Don't worry about this - Interview studying and what's actually relevant on the job have been divergent for a long time. It sucks, but that's just how it is. Learn whatever temporary tricks you need to pass the interviews, and then unlearn that to succeed on the job (learn from Taro instead 🧠).