It is fine for medium size applications, you do have to register all events (goals) on the website before you can use them [0]. I have written the Qt/QML plugin for plausible [1], I don't think predefining them is too bad.
Ah, neat, ok! I'll take another look. For now I've been testing out Posthog (https://posthog.com). They seem more focused on this use case - they let you do arbitrary queries and build graphs over all event data without having to predefine goals or anything, and they have an open-source & self-hostable version, in addition to a EU-hosted cloud option. Now that GA is so clearly dying (finally) it's an exciting space!