Though the game does try to connect to the internet when you start it up for the first time so boo for that
Probably Unity Analytics. System information, IP config, play time and what ever else the dev wants (Ie. started a certain event/quest), all attached to a single unique user ID. Could also be Unity Ads but it seems to be rarely used at least on PC.
It's a must to block nearly all Unity games these days, unfortunately. UPE is more advertisement and datacollecting than game-engine at this point.
All "Unity" games seem to do that.
Games developed with Unity Personal Edition('free') are forced to have the Analytics plugin enabled, and I believe it is required along with the Ads plugin if the developer wants to make use of Unity's online features, for instance the IAP plugin.
I don't really remember what it was called or anything, but there's some way you can opt out of using it completely. Probably as a GDPR thing.
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If I remember correctly you can't fully opt-out across all Unity games, but rather each individual game.