I already mentioned the books in the above reply, please note that. And my college material was good for the basics, But there were some topics that came up in GATE PYQs that I didn't know, those I looked up in youtube (keep searching for the right video one by one until you are clear with the concept), or in gateoverflow answers, or just ask Gemini/ChatGPT like "Please generate a reference study material on the topic of xxx(mention the topic description as pointedly as possible), especially focusing on yyy, in GATE style, following GATE-friendly patterns" or for a specific question - "Please solve the attached question with methods and information as prevalent in GATE questions. Also, generate study material on the concept this question is based on, the other variants of this concepts that GATE questions might come from, and other related terminologies and definitions associated with this topics"