Release Channels in the Meta Horizons Store require signed release mode Keystores.
Unreal Engine's packaging system expects your keystore to be in your project's Build/Android subdirectory.
Keystores are files that are signed and unique and are required for app distribution on the Google and Meta online stores.
If you lose your keystore, you will not be able to upload updates to your app in the Meta Horizons Store -- you will have to create a whole new app entity on the store, recreate your store's application page, and if you have any existing customers, you'll have to manually re-invite them all back in, which is a very tedious and error-prone process.
There are technical ways to recover and rebuild a lost keystore, but the process is not trivial and will require the cooperation of meta to get a copy of the data you need -- stories in the field make it clear that Meta is not always cooperative in retrieving this data. Their cooperation is, however,