The definitive answer is NO – Lyra could not possibly have been done in 100% Blueprints.
That being said, it could MOSTLY be done in Blueprints.
Because Lyra uses Gameplay Ability System, an extremely powerful multiplayer action framework, it does require C++ for some parts. However you could probably implement your own custom GAS system to get around that issue.
C++ and BP are intended to be used together, not just one or the other. That’s part of the beauty of Unreal Engine.
Learn C++. You will be a much better developer if you do.
Good luck. 