Wooden frame garage window bricking

Hi everyone. I have a single brick layer garage with a wooden frame window which I wanted to brick up. Are they usually supported at the top with a metal support because I can’t see one. Or would the builder have inserted the frame/window first and then bricked above it? Garage is just one storey and probably built in the seventies. Flat bitumen roof above. Thanks for your time.

Probably just sitting on the frame. A steel angle is the usual lintel in this situation and you'd surely see that.

Back in the 70s, builders almost always laid the bricks right on top of the timber frame without putting any steel in, so the frame is likely holding those top bricks up.
Definitely prop up the bricks/roof above before you rip the frame out, or that top section might drop on you. When you brick it up, pop a lightweight concrete lintel across the top and tooth the new bricks into the old wall every other row so it ties together properly.
Gently knock away a bit of mortar at the top corner to check, but 9 times out of 10 in a 70s garage, it's just sitting straight on the wood.