@robone tried this out and was able to enable the flag with:
docker run -d --name=grafana9 -p 3000:3000 -e "GF_UNIFIED_ALERTING_SCREENSHOTS_CAPTURE=true" grafana/grafana
@robone tried this out and was able to enable the flag with:
docker run -d --name=grafana9 -p 3000:3000 -e "GF_UNIFIED_ALERTING_SCREENSHOTS_CAPTURE=true" grafana/grafana