GLP-1 is a class of drugs (or molecules). The first known GLP-1 was pretty much just a synthesized version of a naturally occurring compound from the Gila Monster’s venom.
Semaglutide is like a 2nd generation GLP-1 and there are 3rd generation ones in development right now
Semaglutide and co are "GLP-1 receptor agonists" that behave in a similar way to the naturally occurring hormone GLP-1.
We can't give people GLP-1 itself because it breaks down really fast and you'd have to provide it continuously, so we use ones that effect the body the same way over a long period of time.
Semaglutide is like a 2nd generation GLP-1 and there are 3rd generation ones in development right now