Google Play Protect may flag Ac Market because it allows mods. You can disable it during installation:
Safety is paramount when dealing with mods. The new version includes an integrated scanner that checks every APK against a database of known malware. If a file is flagged, a red warning banner appears. This proactive approach makes one of the safest places to download high quality modded content. Ac Market 3.2.3 For Android - Download High Quality