Hi,
I'm new in the forum and I'm planning to buy a bike. I don't know a lot about bikes and I've got this doubt about frames. Are frames of a lineup of a specific brand shared among all models of it? I mean, like for example, the frame in the Giant Talon lineup (0,1,2,3) is shared among all models or is different.
Thanks,

"Generally" yes. within a model line, frames are usually the same material; higher cost get you better components. Geometry will change a bit, especially with small frame sizes. In the case of the Talon Series, lower numbers (higher prices) get you better forks and other components. You can get specifics by viewing this video:
Sometimes as you move up a cost frames will make a jump. I know road bikes so a few examples are with Trek Domane for example, you start with an aluminum frame and at some point as price goes up you jump to a carbon fiber frame. In the case of Orbea Orca you get the same frame from about $2000 to $3000, getting slightly better components along the way. And then at about $3,400 you get a slightly higher modulus carbon frame.

Bottom line is that you have to do your research. And anyway, bike manufactures sometimes switch out components which differ from what's on their websites just because they can't get a hold of one specific component and they'll substitute a similar level component from a different manufacturer.

As already stated, the different "levels" of a given model usually share the same frame, but there are exceptions, so read the spec sheets and geometry charts just to be sure. In the case of the 2022 Talon lineup, they all appear to be the same.

Usually the highest end model will have frame that is “better” material being lighter,stiffer, more comfortable, etc.
examples are S-Works and HiMod. Hard to say whether the higher price really makes a meaningful difference.