na-adjective
hands-off; indifferent; spectatorial
Describes an attitude of observing from the sidelines without getting involved, often with a nuance of detachment or indifference.
彼は会議で傍観的な態度をとった。
He took a hands-off attitude at the meeting.
傍観的な立場から意
It's easy to give an opinion from a spectatorial standpoint.
無関心 means 'indifferent' or 'apathetic' with a stronger sense of lack of interest; 傍観的 emphasizes the act of watching without participating.
Compound of 傍観 (ぼうかん, 'looking on') + 的 (てき, '-like, -tic'). The exact historical derivation is uncertain, but the word follows a common pattern for forming adjectival nouns from Sino-Japanese nouns.