From your photo I think the bike is a bitser, and without decals/names/markings its very hard to identify.
The front fork is clearly labelled Giant and has straight tines so its relatively modern. Possibly a carbon or aluminium alloy fork, it doesn't look like a steel fork. Fork is also painted completely different to frame, so they're not originally together. Fork is also threadless at the top, which is quite modern. The frame would have had a quill stem when new.
However the hoods and brake levers are 80s or possibly early 90s. They're not combined brifters, the shifters are on the downtube which is completely 80s.
The horizontal top tube looks 90s when considering its aluminium alloy. Thicker walled aluminium was used when it was a new material for framebuilding, and hydroforming wasn't possible so strength was added with bulk.
The rear wheel cutout in the seat tube is for aerodynamic reasons - it smooths the airflow a bit, but the main advantage was to permit a shorter wheelbase while retaining 700c wheels.
The road double chainrings are not a compact, instead they're quite close together in size. Not sure what that implies, other than few hills.
Identifying steel is easy - touch it with a magnet (like an old hard drive magnet) and see if it attracts. Aluminium or titanium won't attract a magnet. To tell Aluminium from Titanium is harder - neither require painting. Titanium will spark a lot, bright blue/white when touched with a grinder, and aluminium won't really spark at all.
If you can get to a bare piece of metal, apply a moist cathode (paper towel) to the positive-attached metal. 9v should do to get a slight tan tinge. 18v (2x9v batteries) will take you to dark violet. Some of these requires taking off a patch of surface coating, so not a first option.
Heres a 1998 mongoose road bike that shares a lot of features with your frame's design. This one is aluminium, and has the original fork still.