Hi what Brand is this fixed-gear bike?

Based on the downtube logo this is a "FIX-D" brand of fixed-gear bicycle.

These are low-spec bikes sold through Target and aliexpress. The frame is Steel.

Someone has removed the front brake and brake lever, and the front wheel's QR lever is in a bad angle. Can't comment on the rear of the bike. The saddle on yours is from a Diamondback as well.

The front tyre has been changed at some time, and its possible the front wheel is different from stock too.

The left hand pedal is busted in half - that's not safe to ride and needs to be replaced. Generally you have to buy pedals in pairs, check elsewhere on this site for how to fit and the pitfalls/gotchas.

I removed the 27-inch tag because this bike has 700c wheels, which are 622mm.

Source: https://www.propertyroom.com/l/magna-fixd-road-bike/10178232