insofar vs to that extent

insofar and to that extent both are adverbs.

Word	Noun	Adjective	Verb	Adverb
insofar	No	No	No	Yes
to that extent	No	No	No	Yes

As adverbs, insofar and to that extent are synonyms defined as:

Other synonyms of insofar include in so far, so far, to that degree.

insofar (adverb)	to that extent (adverb)
to the degree or extent that	to the degree or extent that