Your friend is correct: we find information on the computer, we also move files and install programs on the computer. It is similar to how we say that we watch the news on TV, listen to music or a talk show on the radio. In all these cases we are not talking about the physical objects themselves but their concept or idea. (It doesn't really matter what actual TV set, computer, or radio receiver we use to find some info, watch a show, or listen to the news.)

You would use "in the computer" if you referred to the physical object: There is 8 GB RAM and 256 GB hard drive in the computer I am thinking of buying.

Also, of course, we use "on" if we talk about something laying on top of the physical objects, the "body" of the computer:

Ann: "Did you see my book?"

Bob: "Yes, it's on the computer."

P.S. No, you don't have to share your research with us.

Your friend is correct: we find information on the computer, we also move files and install programs on the computer. It is similar to how we say that we watch the news on TV, listen to music or a talk show on the radio. In all these cases we are not talking about the physical objects themselves but their concept or idea. (It doesn't really matter what actual TV set, computer, or radio receiver we use to find some info, watch a show, or listen to the news.)

You would use "in the computer" if you referred to the physical object: There is 8 GB RAM and 256 GB hard drive in the computer I am thinking of buying.

Also, of course, we use "on" if we talk about something lying on top of the physical objects, the "body" of the computer:

Ann: "Did you see my book?"

Bob: "Yes, it's on the computer."