MikeJones how about reading the docs on AWS website ? 🤷♂️ https://aws.amazon.com/lightsail/features/
Sounds like a managed VPS to me, while EC2 is unmanaged VPS. The page says you can move your lightsail VPS to EC2 if you want.
So I guess as far as Flarum installation is concerned, it will work exactly the same. It's all the remaining of the server management that will be different.