Is Internet Access Required?

I have my Ender 3 V2 in my airplane hangar which has no internet access. Will OctoPi work if I just connect both my laptop and Pi to a router?

Yes it will work, if both devices are connected to a network, it doesn't need the internet. You will lose some 'quality of life' features such as built in software updates, installing plugins, and of course specific plugins that need to connect to the internet to do their job. Updates & plugins could still be installed manually by downloading the necessary files and manually uploading them, it would just be inconvenient.