This article seems to imply that Holyrood has been challenged before about trying to create laws not in line with UK laws.
But this time them were proved able to do this - well in an adjusted way.
The Holyrood bill was first passed unanimously by MSPs in March 2021, but after a challenge from UK law officers, the supreme court ruled that four sections required amendment because they went beyond Holyrood’s powers.
The supreme court ruling meant it was necessary to narrow the scope of the bill to fit within devolved powers, which Somerville described as “deeply disappointing”, though the Scottish Conservatives’ deputy leader, Meghan Gallacher, countered that it was a result of Scottish government “incompetence”. Other MSPs urged the government to learn lessons from a fraught legislative process ...
https://www.theguardian.com/politics/2023/dec/07/holyrood-passes-revised-bill-on-childrens-rights-after-uk-challenge
I wonder if the GRR could be "narrowed" - but doubt this will happen as (1) it could water down "trans rights" and (2) would be an acceptance that Westminister can "dictate" to Scotland.