The unique device identifier can be found in game logs (no need to run UnityDeviceUniqueIdentifierHarness)

[SergejKiller]

The offline mode section can be extended with the following text:

Alternatively this identifier can by found in the `s` file immediately after `"deviceid":` text located in `%APPDATA%\..\LocalLow\Team17\Overcooked2\Unity\local.fa9b92e3adcf1c14a809fbd66253e0a8\Analytics\ArchivedEvents\*\s`.

[Stargazed-Dreamer]

I don't think that's the unique device identifier because I have the same " unique device identifier" as your's (at the same path).What's more, I know lot's of online friend don't have that folder "Unity\local.fa9b92e3adcf1c14a809fbd66253e0a8"