I should mention that we have a ton of SDKs (see https://posthog.com/docs/libraries) for back end frameworks and languages, so if you wanted to use PostHog without any client-side JS you could send pageviews and other events manually, but for the vast majority of people it makes more sense to use our JS snippet.
Hijacking this comment to share the roadmap for web analytics https://github.com/PostHog/posthog/issues/18547. It's very much in the launch-early-and-be-embarassed phase, but I would love to hear any feedback or suggestions that people have, particularly if you're already a PostHog user.