The verdict
If you have no analytics yet, I'd pick Plausible first. It gives the whole team a shared set of numbers, and you will use it every week. If you already have numbers, and a page converts badly, I'd pick Clarity. A few real sessions often show the cause within minutes.
They do not compete, so on a small site I'd run both. Clarity costs nothing, so the only price is your time and some care with consent and masking of sensitive fields. Neither replaces a product analytics tool for in-app behaviour. If you need on-page surveys, look at Hotjar, since Clarity shows what people did but does not ask them why.