Is the basic premise of transcendental idealism still valid?

No meat...just package. ...

FBM wrote:

The noumenon required by Kant is an entity/form not perceived by the senses, much like a god or spirit or soul.

No, not at all. Kant's relied on noumena as a way to explain the persistence of reality that did not rely on the existence of an omnivoyant being - thus refuting Berkeley's idealism.

Noumenon
Philosophy
Written by: The Editors of Encyclopædia Britannica
Noumenon, plural Noumena, in the philosophy of Immanuel Kant, the thing-in-itself (das Ding an sich) as opposed to what Kant called the phenomenon—the thing as it appears to an observer. Though the noumenal holds the contents of the intelligible world, Kant claimed that man’s speculative reason can only know phenomena and can never penetrate to the noumenon. Man, however, is not altogether excluded from the noumenal because practical reason—i.e., the capacity for acting as a moral agent—makes no sense unless a noumenal world is postulated in which freedom, God, and immortality abide.

Henry Allison In Kant's Transcendental Idealism, Henry Allison proposes a reading that opposes Strawson's interpretation. Allison argues that Strawson and others misrepresent Kant by emphasising what has become known as the two-worlds reading (a view developed by Paul Guyer). This — according to Allison, false — reading of Kant's phenomena/noumena distinction suggests that phenomena and noumena are ontologically distinct from each other. It concludes on that basis that we somehow fall short of knowing the noumena due to the nature of the very means by which we comprehend them. On such a reading, Kant would himself commit the very fallacies he attributes to the transcendental realists. On Allison's reading, Kant's view is better characterized as a two-aspect theory, where noumena and phenomena refer to complementary ways of considering an object. It is the dialectic character of knowing, rather than epistemological insufficiency, that Kant wanted most to assert.