When using Abnormals Core 3.1.0, you cannot use the boofalo vest's inflate ability. I tested with Abnormals Core 3.0.6 and it worked with that

I'm unable to reproduce this issue with Abnormals Core 3.1.0
Make sure there aren't any keys conflicting with the Booflo Vest, so first try changing the keybind.

I'm having the same issue.

Try changing the keybind and see if it works. If it works, then there's a key conflict.

isn't it just the jump button? I'm not seeing any specific keybind for it.

It's space by default. The keybind is called Booflo Vest Activate.