Viññāṇa anidassana

(Consciousness that is not becoming visible) 

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Nidassana = Nidarśana

Viññanam anidassanam = Consciousness that is not becoming visible (invisible) [that is not manifested].

निदर्शन nidarśana [agt. nidṛś]
निदृश् nidṛś [ni-dṛś]
√ दृश् dṛś or dṛṣ [var. paś]
- to see, behold, look at (RV., AV., ŚBr.)
- to be seen, become visible (RV., AV., ŚBr.)
- to be shown, manifested (MBh.)

It corresponds to viññana nidāna, when there is no more establishing of consciousness.
See here.
That is to say:
When there is no more maintenance of consciousness (SN 12.11 - SN 12.39)
When there is no descent of consciousness in Nama-rupa (SN 12.59), and the ensuing process.

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Not only is viññāṇa nidassana not visible; but to be beholden, it should not become visible (in the process of descending into the "world" of senses).

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Ajajjaraṃ dhuvaṃ apalokitaṃ,
Anidassanaṃ nippapañca (https://justpaste.it/3f6gs) santaṃ.
Not decaying, permanent, to behold (अवलोक् avalok) unmanifested, free from development of/in the sensory world, peaceful.
SN 43.44

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Ayañhi, bhante, ākāso arūpī anidassano.
Tattha na sukaraṃ rūpaṃ likhituṃ, rūpapātubhāvaṃ
Because space is without form and invisble/non-manifested; it is not easy to draw pictures there or make pictures appear there.
MN21

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