The current pre-release of the client ("pioneer" in the version) is only compatible to itself. So you can only play with other testers. Please be aware!
There was a bug with the new client version for players first downloading the client. It should be fixed now in the hot fix release found at https://github.com/FAForever/downlords-faf-client/releases/tag/v2022.1.1
Sorry for the inconvenience