You could try looking at the player files; if a player file is there, it is obvious that they have joined the server at some point as the game creates a new file for every new player that joins.
You can then compare that against a copy of the player data folder to get the delta; any new players that has joined since you last "cleared" (made a backup) it.
It's not a straight-forward as you've probably noticed after some experimenting, even though it's the same way as Java, just with a few more steps.
First, look up your server's WorldDB
You'll need a copy of your server's
world folder. Copy it while the server is off. If you copy while the server is running, it is likely it still has a lock on the database and your resulting copy is "corrupt".
First, grab a Bedrock world viewer. The only one out there that works (that is noob-friendly) is Universal Minecraft Editor.
When you open your world, you'll be greeted by a bunch of random GUIDs.
If you want to edit save data, the one you only need to care about is those starting in
server_<GUID>. Each entry maps exactly to one player.
But of course a player can access the server by any number of devices.
Next, convert that gobbolly goop into usable usernames.
If you look in the ones that don't end in
server_<GUID>, you might notice three keys;
MsaId (Microsoft Account ID),
SelfSignedId (Cryptographic combination of the
ClientId) and the save data (
Unfortunately this is the furthest you can go due to security policies set by Microsoft. Unless all your users are in your own domain (as opposed to random Xbox Live users), Graph API is useless.
In case, authenticate and call:
Your best bet is to look at the console for any messages beginning in
Player Connected: <Username> xid: <xBox numerical ID> or
Player Disconnected: <Username> xid: <xBox numerical ID>.
Unlike Java Edition where everything is wide open - Microsoft Accounts are security first. A handy way to keep logs (because Bedrock doesn't have logs for some reason) is to just redirect
bedrock_server.exe > %DATE%%TIME%.log