The relevant usage is the one classically labelled 'adverb' shown by say CED:
that adverb B2 as much as suggested:
She's too young to walk that far.
It wasn't (all) that (= very) good.
Note that 'so' can be substituted for 'that' in the first example, and without 'all' in the second.
This would appear to license the ' ... that + adjective + that ...' usage.
But it sounds so clumsy that it must be considered unidiomatic. This is brought out by these Google Ngrams for so simple that / that simple that; so far that / that far that; so small that / that small that; so heavy that / that heavy that. (Yes, there are 8 ngrams there!)
Omitting the second 'that' improves the situation somewhat, but 'so simple anyone could pass it' remains the favoured choice, as these Ngrams suggest.
'It was that simple, anybody could pass it!' is not unknown in informal/colloquial registers.