Linq2Couchbase still hasn’t been fully updated to be compatible with SDK 3. We’ll probably be released a beta shortly, but until then you’ll have to build the DLL from source code in GitHub.
Usage is pretty easy, just make sure to call AddLinq when you build your ClusterOptions.
var options = new ClusterOptions().AddLinq();
// Set other settings
After that, you create a BucketContext passing in the IBucket instance you want to query. For how to get that, refer to the standard SDK 3 documentation. You’ll probably use the DI infrastructure if you’re on .NET Core.https://docs.couchbase.com/dotnet-sdk/current/howtos/managing-connections.html#connection-di