The Galaxy A02 came with Android 10 out of the box and has since been upgradable to Android 11. If you have ever tried looking for Android 10 or 11 firmware for the Galaxy A02 smartphone, you would have noticed the sites offering the files weren’t Samsung. Some sites seem official enough because over the years they have developed a reputation for constantly offering Samsung firmware files such as SamMobile, but it’s still not a site owned by Samsung.
If you’re happy installing firmware from SamMobile, then go right ahead. but it’s risky. There is no guarantee they haven’t made a mistake by offering you the wrong link. If there is no official site offering Samsung firmware files, and you don’t want to trust a site offering the files, you can install a free Samsung firmware update tool that will download the file’s directly from Samsung’s servers.
If you don’t want official firmware, there is always a custom ROM if your device is popular enough. The Galaxy A02 will likely have custom ROMs available for it in time, but it’s still a bit new. Some people are already asking for custom ROMs for it though so it’s only a matter of time.