I've interviewed countless polyglots about their language learning methods, and so far everyone's methods have been wildly different. From more manual transcription based approaches, to traditional learning, to algorithmic spaced-repetition based. However, there are components that all methods seem to share.

Direct engagement with native material. This one is a non-negotiable, and the one most overlooked by beginners. Learning a language is only half the battle; the other half is learning to use the language. Mass exposure to YouTube, podcasts, TV, movies, books & more.

Some use of a formalized spaced repetition system. All learning is a matter of understanding things, and reviewing it periodically. Using an SRS allows you to do this as efficiently as possible, and while only about half of the polyglots I know keep up with using an SRS (which is still a large portion!) every polyglot I interviewed routinely uses it at some stage in their learning.

Unmaintainable amount of time spent on research and management. The last thing that I noticed when asking about people's method was the amount of time they spent on 'busy-work'. Translating, transcribing, dictionary lookups, grammar research, conjugating, flashcard sourcing, flashcard creation, deck management, anki configuration, note taking, spreadsheets, time tracking, and so much more. Almost all of which could be automated, if implemented properly.