Is Attack on Titan Finished? Yes — Complete in 34 Volumes
Yes — Attack on Titan is complete. It ended in Japan with 34 volumes; the final volume came out in June 2021. All 34 volumes are also out in English (final volume: October 19, 2021).
Everything below reflects the Japanese edition — the source of truth that runs months or years ahead of English releases — computed from official publication records.
Volumes in Japan: 34 (latest: 進撃の巨人 : beginning 34, 2021-06)
Next volume in Japan: not yet announced in Japan.
Status: Yes — Attack on Titan is complete. It ended in Japan with 34 volumes; the final volume came out in June 2021.
Serialized since: 2010
English edition
Latest volume in English: Vol. 34 — October 19, 2021
English dates: volume lists on English Wikipedia (CC BY-SA). The estimate uses the recent English release pace and is not a publisher announcement.