If you allow for miniseries, then something like Roots (1977) would be one of the older ones that I have seen.

Twin Peaks broke the episodic TV paradigm making way for longer stories being told via this medium. It still got loads of filler, especially in the second season parts without Lynch, but Rome wasn’t built in a day (/chuckles).

@Skavau Roots, Holocaust, V… I recall “Silk Stockings” not being high quality but it was the start of cable shows.