Bonjour,
Ideally it would be possible to register a webhook to get notified when something (anything) happens on a forge. Such a webhook unfortunately does not exist and fedeproxy will have to maintain webhooks for every federated project.
Although not documented, the web interface suggests it is either possible to set a webhook to all events or specific issue events.
More information about Gitea webhooks: it has three tiers of webhooks (like gitlab) we have repo, org, and system-wide, and as you have already discovered filtering of event type is possible.
It saves me the trouble of investigating, great 
All Events are system wide events (i.e. repo creation, repo deletion, etc.) ? I’m a little confused because it seems to be possible to register a webhook in a repository about repository creation.
For repo level webhooks, the repo event would only send a repo delete hook, as like you said you can’t add a webhook for repo creation to a repo that doesn’t yet exist. But for org and system-wide webhooks it would trigger on repo creation.