It's common in action games for boss monsters to be much larger than the player character, even when they are allegedly supposed to be a normal member of the same species as the PC. This has obvious gameplay benefits like making it easier to see what the boss is doing.
But these games vary in how they treat the bosses' size from a lore perspective. Are they actually that big, or is it just a game mechanic?
On one end of the spectrum, in Guild Wars 2, there are certain raid encounters where the boss is a story character who appears at normal size in every other part of the story but grows to jumbo size at the start of the raid encounter and shrinks back down at the end. Clearly the size is for gameplay purposes only and not meant to be interpreted as literally happening.
Sekiro: Shadows Die Twice is in the middle. Bosses like Gyoubu Oniwa appear huge despite presumably being normal humans, and we never see them at normal size. Isshin towers over Sekiro even when you're just talking to him as an NPC. But the lore doesn't really provide much reason for them to be that big, which leaves me thinking it's still not supposed to be understood as literal.
The other end of the spectrum is Elden Ring, where bosses like Rennala and Morgott really are supposed to be that big. In the lore they're demigods, a cut above mortal men, and their lairs have giant-sized furniture matching their depicted size.