TL;DR look at the bold text.
As you know, the plugin uses the Google Analytics Measurement Protocol (an open web API) to provide a 100% cross-platform analytics solution, not dependent on any closed source pre-built SDKs. The Measurement Protocol for UA is a completely different protocol than the GA4 version.
At the time of writing, the current state of the Measurement Protocol for GA4 is not suitable for replacing the default SDKs provided by Google. This means that we cannot currently provide an integration for GA4.
We're in contact with Google and we're also analyzing possible workarounds and alternatives. But at the moment we can't guarantee support for GA4, since this depends on technologies provided by Google.
For the Measurement Protocol to work as a replacement for the default SDKs provided by Google, it must support what Google calls server-to-server (S2S). Here what the official documentation says about it: https://developers.google.com/analytics/devguides/collection/protocol/ga4#full_server-to-server
While it is possible to send events to Google Analytics solely with measurement protocol, only partial reporting may be available. […] Some event and parameter names are reserved for use via automatic collection and cannot be sent through the measurement protocol.
The first appearance of this note should likely be dated between July-August 2022.
This is different than UA, that is providing a S2S implementation supporting all the events and parameters.
We periodically tested the state of the Measurement Protocol for GA4 and here is a summary of the results. Please note that it's possible that something changed in the mean time.
The most critical limitation at the moment is the impossibility to log the “standard properties” handled by GA4, since they feed all the pre-made reports available in the GA4 system. Without them, all the standard reports in GA4 will remain empty. A blocker for anyone looking for an analytics solution.
We informed Google of the limitations we found and they are aware of them. For some of the reported issues, they have internal Feature Requests filled. But we don't know if and when they will be addressed.
If you want to raise the priority of those feature requests, helping Google to have a better idea of the number of affected developers, you can reach the Google Analytics team at https://developers.google.com/analytics/help/#contact-us.