I think this is likely down to one of three things, so let’s see if any of the following works:
The endpoint you’re pointing at is the endpoint for the Iglu Webhook. There’s a more generic endpoint we could try - try replacing com.snowplowanalytics.iglu/v1 with com.snowplowanalytics.snowplow/tp2 in your endpoint.
I think it used to be required to include the port number in the URL, but now it’s not. Try removing :8080 (so eg. http://<EXTERNAL_IP>/com.snowplowanalytics.snowplow/tp2).
If neither of those work, then my main suspicion would be the network rules for the IP. Indeed in your screenshot ‘Connect’ seems to be set to ‘SSH’.
I’m not massively familiar with where to find/how to configure network rules on GCP, but the collector endpoint’s IP address should be configured to accept traffic from the internet. Typically, it’s configured with ‘allow all’ - since it needs to receive data from the users’ devices, which could come from anywhere.
Honestly, my suspicion as to what’s going on is stronger on point 3 since you’re getting timeouts. I would expect 1 and 2 to return a 4XX if misconfigured - however those will be easier to check quickly.