Since "1080p" usually refers to high-definition releases, you need a subtitle track that matches that specific version's timing. Recommended sites include:
Podnapisi: Great for community-verified and perfectly synced subtitles. 2. How to Add the Subtitles subtitle Outlaw King 1080
YIFY Subtitles: Ideal if your 1080p file is a "YIFY" or "YTS" release, as these are pre-synced for those versions. subtitle Outlaw King 1080