Only after witnessing the Great Dao true meaning could one begin "Dao Foundation Perfection." For every Great Dao, if the cultivation methods differed, then the means of "Dao Foundation Perfection" would differ as well. Yet in essence, they were the same: one had to make one's own Dao Fruit Auspicious Cloud increasingly similar to the Great Dao, until one could use it as a foundation to intercept the Great Dao, condense a Dao Seed, and unite with the Dao in truth. Thus, the Daoist Sect mostly condensed the Three Flowers Above the Crown, while the Buddhist Sect generally severed the three corpses of good, evil, and attachment.
Many Half-step Golden Immortals, due to flaws and imperfections in their own cultivation methods, found it difficult to perfect their Dao Foundations after witnessing the Great Dao true meaning. They either had to spend decades or millions of years listening to teachings under the Lord of Creation or the corresponding Dao Ancestor, deducing and perfecting their own methods, or they had to seek out a flawless supreme cultivation method and use its Perfected Dao Foundation as a reference.
As for precisely how to "perfect the Dao Foundation," there was one obvious difference between Innate Great Daos and Acquired Great Daos. Cultivation methods for Innate Great Daos often sought nothing externally, or, if they did, took nature as their teacher. Cultivation methods for Acquired Great Daos, on the other hand, often carried a strong air of achieving things through human effort.
On this point, Shi Xuan thought of Qianxuzi from Taixu Temple. He needed to nurture illusory Three Thousand Great Daos from the cultivation methods and Immortal Techniques of others. Only when all Great Daos apart from the Dream Dao were complete and bore fruit would his Dream Universe Dao Foundation count as perfected.