How to run both
Leave Plausible exactly where it is. Add the Tiny Funnel script tag next to it, then open your own site in setup mode and click through the flow you care about: the landing page, the pricing page, the signup form, the welcome screen. That click-through is the funnel, and there is no event code to write and no goal to configure first.
Nothing about the two scripts conflicts. Both are cookie-less, both are first-party, and they are answering different questions, so keeping both is not a transition state. It is a reasonable place to stay.
The layer Plausible chose not to build
Plausible is deliberately aggregate. That is a considered privacy position and it suits a site dashboard well. It also means that when a number moves, the individual stories behind it are not in the product: user journeys will show you the paths visitors take in aggregate, and it stops there.
Tiny Funnel keeps that layer. Any visitor in the funnel can be opened and read end to end, return visits included, down to the step where they stopped.
The same layer is what lets a step mean more than a URL. A step can be a page state ("the element says subscribed"), a click, or an event your backend posts when the money actually moves, attached to the visitor who caused it. A visitor the script tag has never seen cannot be started by a server event, so the journey always begins in the browser, but it can end in your webhook handler.
The short version
Keep Plausible for the site. Add Tiny Funnel for the funnel: where each cohort of visitors comes from, how far they get, and which of them buy. Adding it costs $10 a month per funnel, and neither tool uses a cookie.
