https://www.pcgamer.com/total-war-three-kingdoms-trailer-shows-more-realistic-records-mode/

So far we've seen plenty of the Total War: Three Kingdoms Romance mode but little of the more realistic version of the campaign, called 'Records'. It sounds like this mainly changes the power of heroes in battles. Instead of being lone warriors capable of fending off entire units, heroes fight as part of a unit of fighters. They are also more vulnerable than they are in Romance mode.

According to the Sega press release battles in Records mode tend to go 30 percent longer. "This comes down to units becoming fatigued more quickly, reducing the damage they dish out as they tire. The result is an increased pressure on player choices—knowing when to invest energy and how to maintain an advantage."