Especially for short sections of marked trail across rock, passable to typical people, I would still mark it as path/footway.
And would treat marks on rock (smoothened rock, vegetation removed, lichen scrubbed or trail signs) as sufficient to overtake “has no reality on the ground”. See say File:Krywan podejscie.jpg - Wikimedia Commons or another view showing marks on rock (also on top, where solid rock is present).
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But note that there is https://wiki.openstreetmap.org/wiki/Tag:highway%3Dno has already over 2000 uses
However, occasionally, there may be ways that one would expect to be highways, but are not. In this case, highway=no can be added to explicitly indicated to other mappers and data users that there is no highway here. This allows us to distinguish between the case of a highway type being unknown and needing to be determined, and the case of the way being known not to be a highway.
For example, in the UK, there are sometimes legal Rights of Way that are inaccessible, resulting in a legal highway that is not physically present or usable on the ground. Due to administrative errors, unauthorised constructions or lack of maintenance, the official line of a legal route may pass through dense woodland, though walls of a building a building or though a lake. highway=no can be used in these cases to explicitly mark the way as not being a highway, while still recording the official line.
This tag should not be used to highways that physically exist but have restricted access. This use of this tag for such cases is deprecated, in favour of highway=* + access=no.