here is a quick how to get Google Camera working in Oreo:
1. Install Magisk following this howto
2. Install modules camera2api-enabler.zip and magisk-permissive-script_v1.1.zip
3. Install your choice of Google Camera. I just tried out GCam5.1.018-Arnova8G2-V1.2 with these settings
Note: I don't know if this is the best Google Camera version for Oreo out there. If you have other suggestions, please let me know.