The kubectl fdb plugin 1.+ should only be used with the operator 1.+ version in your case you should make use of an older version of the kubectl fdb plugin. The v0.51.1 version of the kubectl fdb plugin would be the last version that supports versions below 1.+ Release Release v0.51.1 · FoundationDB/fdb-kubernetes-operator · GitHub. In general the plugin should work for the same major releases but I would suggest to keep the operator and kubectl fdb plugin the same or at least close.
But the provided error Error: exec format error is probably unrelated to the version of the kubectl fdb plugin and you should check if you actually downloaded the correct binary for the plugin (correct OS + architecture).