Firebase -'isDirectChannelEstablished' is deprecated: FCM direct channel is deprecated, please use APNs channel for downstream message delivery

It sounds like you should just remove that line. According to the API documentation:

When set to YES, Firebase Messaging will automatically establish a socket-based, direct channel to the FCM server. Enable this only if you are sending upstream messages or receiving non-APNS, data-only messages in foregrounded apps. Default is NO.

So, unless your app is doing either of the things described here, it's not necessary. According to the release notes:

Deprecated FCM direct channel messaging via shouldEstablishDirectChannel. Instead, use APNs for downstream message delivery. Add content_available key to your payload if you want to continue use legacy APIs, but we strongly recommend HTTP v1 API as it provides full APNs support. The deprecated API will be removed in Firebase 7 (#4710).