Reaching the Billionaire status isn't a child's play, and although so many people want to reach this point, they do not know the problems to solve to become a billionaire. Do not forget that when you solve problems, you make money either directly or indirectly. Elon Musk, Jeff Bezos, Bill Gates, and many more billionaires are solving problems, and as such people see their business as being innovative and solving problems and that is why they have hit and remain at that billionaire status.
You do not have to pick the world's biggest industries as these industries are already dominated by giants who have the money and power to kill their competition. There are a lot of problem in the world which needs solving and if one could solve it perfectly, then one is in money.
Weight loss Pills
If you work from home/remotely, there is a high chance that you will be obese as time goes on as people are getting tired and find it difficult to do exercises. If you can find a solution to this with a pill that will help reduce fat, then you good to go.
Bio Printing
Transplanting is very difficult as people need to find organs for transplant. To solve this, creating a bio-printed organ is going to be a solution that they have been waiting for. If you can solve this problem you are going to be on your way to Billionaire status.
Food Production
The fundamental/basic human needs are food, shelter, and housing, and when people do not even have any other option but to eat. Agriculture and food is the biggest industry in the world as people need to cater for their continuous need food
Conclusion
You do not need to compete with big companies, you just need to pick an industry where you can make a stand and utilize the opportunity available.