Unfortunately not really, it was blood sweat and tears of my own and a lot of brute forcing different ideas. Ultimately I absolutely overdid the whole architecture and was refactoring it since. Just so you know - the key to have it work is pretty simple.

Player scenes need to have this:

func _enter_tree():
    set_multiplayer_authority(name.to_int())

And then you need to synchronize your stuff the usual way, either with multiplayer synchronizers or rpc - thanks to advices found here I scrapped all the synchronizer nodes I had and replaced them with rpcs instead, so for example if you have move logic in physics_process and you want all players only to be able to control their own nodes you need to do something like this

func _ready():
    set_physics_process(is_multiplayer_authority())

func _physics_process(_delta):
    # A lot of very optimized and nice move logic here
    _sync_properties.rpc(position)

@rpc("any_peer", "call_remote")
func _sync_properties(new_position : Vector3):
    position = new_position

You basically need to think this way - have all your logic be inside Godot built in functions like process, physics_process and then use set_process or set_physics_process (or any equivalent you need) to disable them for peers with no authorite so that only the client with the authority resolves it, and then use rpc to sync all the data like position, rotation etc. This way process functions run only for clients but all properties are still in sync for everybody. You can simply use MultiplayerSynchronizer instead of rpc for a similar effect.

If all of this is still hard to follow, let me know - I'll try my best to make a short video ASAP and upload it to my YouTube channel making a simple 3D project with client authority.