Matomo is probably the leading alternative.

I'll in the process of looking alternatives as GA4 is a step back. I suspect alternate analytics companies are going to love Google for this decision.

You might want to check out Simple Analytics as well. From a privacy perspective this is actually a good shout. We classified it as follows:

Matomo looks more like Google and the data is yours. Plausible and Simple Analytics are more similar to one another in the sense that they only collect privacy-insenstive data.

The main difference is that plausible still operates in a 'grey-area' by anonymizing IP addresses for 24 hours. This can be considered fingerprinting.

I am building one (for around 9 years now): https://www.uxwizz.com

The thing is that "GA alternative" is a broad question, as GA has A LOT of features and it's also lacking many features, it depends on what you're looking for and what's your use case.

I really like usefathom.com

Plausible is excellent.

I like and use Clicky.