monitoring – Google Cloud alerting doesn’t allow creating an alert for its own metric

I have Firebase API on GCP, but I would like to get alerts when my API returns error for more than 10% of requests.

Something which GCP already has:

It’s exactly what I need, first problem is that apparently GCP doesn’t understand its own query as it cannot be parsed to builder or promql/mql, which prevents me from importing it to central alert system of grafana.

If I use Google’s alerting system, and have this specific alert in different place then all others, apparently it’s impossible to create ratio queries in GCP alerting tab.

Also for some reason I cannot use one_of(“4xx”, “5xx”) as it dosen’t find responses with “5xx” even tho they are on the chart, but I can use !=200 and it will do same for me.

Is this query useless because I cannot provide alerting for it? What’s the point of creating this metric in this case?