。
It clearly looked like everyone was in attendance.
Literal
Clearly everyone attending [manner-ように] appeared.
明らかに ('clearly / obviously') is an adverb modifying the entire clause. 全員出席している ('everyone is attending') is embedded inside ように見える ('to appear / to look like'). 見えました is the polite past of 見える. The sentence leaves room for doubt despite 明らかに — ように見える inherently hedges ('appeared to be'), creating a subtle tension between 'obviously' and 'seemed.' This is natural in Japanese reporting where speakers maintain epistemic caution even when the evidence is strong.