@nep
more food for thaught
The primary difference between high fantasy and low fantasy is the setting. In high fantasy, the story takes place in a secondary fictional setting that is utterly independent of the real world. In low fantasy, the story takes place in a familiar, real world setting.
The Lord of the Rings by J.R.R. Tolkien aka high fantasy
The Indian in the Cupboard by Lynne Reid Banks aka low fantasy
if we sub out the MC first life being before truck-kun as the real world and they feel like the new world is explainable due to the lack of knowledge or magic then it is a low fantasy. however if they are throw into a world full of magic then it is a high fantasy. just remember to judge from the stand point of what was the primrary world of the narritive and not are own.
in a way you can argue Sword art online is a low fantasy up to the point of how the story unfolds since it is a story of a locked in full dive game but if you where to take the world and setting of aincard as a real world that kirtito is iseka'ed into then you could say it is a high fantasy due to the unexplaible elements that a MC may not be aware of such as the game compand system since those could just be spells to an out sider.