We are aware of the current update to ETS & ATS and are working on getting the multiplayer mod supported for the latest version as soon as possible.
Steam beta settings:
ETS: temporary_1_34 - 1.34.x for unsupported mods
ATS: temporary_1_34 - 1.34.x for unsupported mods
You can find a guide on how to downgrade your game to still be able to play the mod here: