I don't know about this problem because I never played the campaigns for both Reign of Chaos and The Frozen Throne since 2017.
Since I played this legendary game in 2012, playing campaigns are boring than the skirmishes. I only beat The Frozen Throne by using the traditional "God Mode" and "Reveal Map" cheat codes. For Reign of Chaos, I can't because I'm always stuck at "The Culling", which was a major problem for users who didn't play the game using 1.26 or 1.27. At that time when I played the campaigns for the last time in 2017, I'm using 1.24b, which lacks the Widescreen support and had outdated unit stats since it was released in 2009, before switching to 1.26 in late 2018 and 1.29 in late 2019 (when Blizzard released the last WC3 patches before Reforged, which removes the option to make AI heroes learn their abilities).
Anyways, if you want to skip the certain missions on ROC and TFT, you can use the "motherland" cheat code, followed by the specific races and the chapters,
which includes the interludes. For TFT, you must use the "x" suffixes" similar to Brood War (Starcraft). However, it's more confusing because TFT has one missing chapter, which is actually the Secret Level (The Crossing) for Human campaign that can be only unlocked after obtaining the specific item from the third chapter (Dungeons of Dalaran), and the Orc campaign has a lot of chapters, which are actually the sub-maps that can only be activated by walking through the shimmering portals.
If you still confused, you can download the save games which unlocks all chapters for both ROC and TFT.
