Alien life especially intelligent life would have to look like us
Alien life will have to look like us
There are energy and pressure limitations on the kinds of chemistry that are possible, and for life to form you need a period of abiotic chemical experimentation to be occurring in order to establish the building blocks that form the substrate that will eventually form into and become the basis of 'food' for the self replicating molecules that will lead to the first proper life forms.
There is also the extremely relevant fact that the molecules that make life on earth are not only present everywhere we look (water, ammonia, carbon, carbon dioxide, hydrocarbons) but they're also made out of 4 of the 5 most common elements in the entire universe. Hydrogen is over 90% of the universe, helium is around 9%. But then we find oxygen and carbon are at least an order of magnitude more common than everything else further down the periodic table, due to the way elements are formed in stellar nucleosynthesis.
They're also very chemically flexible. Carbon can form compounds with almost anything, and those compounds can be chained with others due to carbon's spare 'room' for chemical bonds. When carbon forms into compounds, most of them are gases that are soluble in water (water being possibly the most abundant compound in the universe, formed from oxygen and hydrogen which are everywhere, and water is so stable that it requires being heated to a plasma for the bonds to break). Silicon, by contrast, forms compounds that are always solids at temperatures where water remains a liquid, and many of them are not soluble in water at all, like its most common compounds: silicates.
We should expect alien life to be made from hydrogen, oxygen, carbon, nitrogen, and probably also chlorine, sulfur, phosphorus, sodium, and other trace elements that we expect to be found on every terrestrial planet. This doesn't mean that they'll have phospholipid cell walls, RNA/DNA, or even amino acids, but even these compounds except for DNA are so simple and their building blocks can spontaneously form under abiotic conditions which have been observed in laboratory and natural conditions, that there's also a good chance that alien life is at least using ATP/ADP and amino acids, just because of the likelihood of these chemicals forming spontaneously and in abundance after a few million years on a planet with the right conditions for them to have spontaneously formed in the first place.