creamy layer sub categorisation of ST scheduled tribes and SCscheduled castes
To understand that whether the creamy layer test is excluded or not for Scheduled Castes and Scheduled Tribes one has to visit the judgements of the apex court and myriad of view taken by the learned judges. For law students and reader this question has been summed by visiting the following judgements and case laws which have deliberated on the issue of creamy layer principle.

In Jarnail singh v. Lachmi narain, 2018 

the court observed referring to the landmark judgement on reservation ,Indira sawhney v. Union of India,1992, that eight out of 9 judges applied the creamy layer principle as a facet of larger equality principle and observed creamy layer to be identified and excluded. But Sc/St was specifically excluded from backward class mentioned in article 16 .

In M.Nagaraj v. Union of India 2006,

the addition of Articles 16(4-A) and 16(4-B) were under challenge on the ground that they violated the basic structure of the Constitution. The court considering creamy layer aspect reiterated that the ceiling limit of 50%, the concept of creamy layer and the compelling reasons, namely, backwardness, inadequacy of representation and overall administrative efficiency are all constitutional requirements without which the structure of equality of opportunity in Article 16 would collapse.

The Constitution Bench in Ashoka Kumar Thakur v. Union of India, (2008) 6 SCC 1.

In this case, Article 15(5) inserted by the Constitution (Ninety-third Amendment) Act, 2005, was under challenge. Balakrishnan, C.J., after referring to various judgments of Supreme Court dealing with reservation, specifically held that the creamy layer principle is inapplicable to Scheduled Castes and Scheduled Tribes as it is merely a principle of identification of the backward class and not applied as a principle of equality .
However, In Jarnail singh v. Lachmi narain 2018 while referring to the question of revisiting its judgment in nagaraj case court denying need to revisit on question of creamy layer said that the creamy layer principle allows Parliament to exclude certain groups from Presidential Lists under Articles 341 and 342. Constitutional Courts can apply Articles 14 and 16 to exclude the creamy layer, as long as they consider relevant factors. The doctrine of harmonious interpretation allows Parliament to include or exclude individuals from Presidential Lists based on relevant factors. The principle of reservation can also be applied to exclude the creamy layer from certain groups. Balakrishnan, C.J.’s statement that the principle is merely a principle of identification is not supported.
Therefore, when Nagaraj (supra) applied the creamy layer test to Scheduled Castes and Scheduled Tribes in exercise of application of the basic structure test to uphold the constitutional amendments leading to Articles 16(4-A) and 16(4-B), it did not in any manner interfere with Parliament’s power under Article 341 or Article 342.

In E.V Chinnaiah v State of Andra Pradesh,2005

the judgment in essence held that the Andhra Pradesh Scheduled Castes (Rationalisation of Reservations) Act, 2000, which it considered, could not further sub-divide Scheduled Castes into four categories, as that would be violative of Article 341(2) of the Constitution of India for the simple reason that it is Parliament alone that can make any change in the Presidential List and not the State Legislatures. Chinnaiah (supra) also decided that the sub-classification of Scheduled Castes, created by the Andhra Pradesh Scheduled Castes (Rationalisation of Reservations) Act, 2000, also violated Article 14 of the Constitution of India.
However laying rest to above contentions the Supreme court in a welcoming judgement by a 7- judge bench, with majority of 6:1 , in State of Punjab And Ors v. Davinder Singh And Ors, 2024 overruled E.V. Chinnaiah(supra) case,

State of Punjab And Ors v. Davinder Singh,2024

The Supreme Court held that sub-classification amongst the Scheduled Castes for the purpose of giving more beneficial treatment to a group in the larger group of the Scheduled Castes is not permissible, by holding that it does not lay down a good law; extent of sub-classification within Scheduled Castes has been held to be constitutionally permissible by law and that while doing so the state has to show the group which is beneficial treatment is provided is inadequately represented as compared to the other castes in the said List; that while doing so, the State will have to justify the same on the basis of empirical data that a sub-class in whose favour such more beneficial treatment is provided is not adequately represented.
Vikram Nath J. , Pankaj Mithal J. , Satish Chandra Sharma J. , Concurring with the opinion of BR Gavai J. in their separate judgements opined that creamy layer principle is also applicable to Scheduled Castes and Scheduled Tribes, and that the criteria for exclusion of creamy layer for the purpose of affirmative action could be different from the criteria as applicable to the Other Backward Classes.
Hence it is a welcoming opinion of the judges just short of authority. The court has clarified that it is under the power of executive domain to exclude the forward class in Scheduled  Castes (SC)and Scheduled Tribes (ST) and constitutional courts can apply articles 14 amd 16 to exclude. The judges of Hon’ble Supreme court of India in Nagaraj ,then in Jarnail Singh v Lachmi Das case, 2018, and ultimately in landmark judgement of State of Punjab and ors V. Davinder singh 2024, have put strong discourses in support of exclusion of forward classes in Scheduled Castes (Sc) and Scheduled Tribes (ST).