Java : JAVA Foundation with Data Structures : https://www.codingninjas.com/courses/online-java-course
System Design : SystemsExpert : https://www.algoexpert.io/systems/product
Machine Learning : Machine learning by Andrew NG : https://www.coursera.org/learn/machine-learning
Competative Coding : Competitive Programming : https://online.codingblocks.com/courses/competitive-programming-course-online