Search "Hasli LMC8.1 Telegram" (Google de-lists these files, but the Telegram channel holds the official, virus-free archive).
Samsung GCam usage is tricky. Snapdragon models (USA/China) are easier to configure than Exynos best config for gcam 8.1
Before applying configurations, you must start with a stable base APK. The most reliable developers for version 8.1 include: Search "Hasli LMC8