I believe the issue isn't specifically with anonymised IP addresses in GA. The problem is that the Google Analytics code is loaded from a third party server and, to do that, this server gets your IP address even if the data sent by the GA code itself contains an anonymised one.

I think it's personal data because you can track a visitor across multiple visits. Based on that identifier you can connect all the other data points from a visitor. I think that's not privacy-friendly at all.

I guess it depends what "anonymised IP address" means. If it's still possible to correlate data from visitors across different websites, they might as well log IP addresses directly.