You won’t find aluminum wiring in modern residential branch-circuit wiring, but in the 1960s and 1970s, aluminum was common. During the 60s and 70s copper prices led homebuilders to use single strand aluminum in homes to cut costs. At the time, aluminum seemed like a reasonable replacement. It kept the costs low and did the job well.
The issue with aluminum is that it oxidizes rapidly compared to copper. It builds up heat and in doing so, is a fire risk. In a laboratory, they couldn’t see the issues arising. However, in the real world, where conditions are imperfect, aluminum wiring is a problem. If you have aluminum wiring, there are two options. One, you may get special connectors or two, you can have your home rewired.