To clarify - AV1 is not an output video format option in ErsatzTV's FFmpeg Profiles, so the AV1 codec will not be used in HLS Segmenter or MPEG-TS streaming modes.
If there are issues playing AV1 files, the issue would be with decoding AV1 input files, in which case ETV media info (found using buttons on movie and episode detail pages) and ffmpeg hls arguments (from ETV logs) would be helpful to diagnose.