Ultralearning is a strategy for learning hard subjects and acquiring skills in relatively short time, popularized by Scott Young in his book by the same name. It applies self-directed learning and intensity while prioritizing effectivity. Since it is self-directed, it is less wasteful in time and effort and is also more flexible. You can do it part-time, full-time, or as an integral part of your current schedule.
There are nine universal principles of ultralearning.
References
Young, S. (2019). Ultralearning: Master Hard Skills, Outsmart the Competition, and Accelerate Your Career (Illustrated edition). Harper Business.