Hi, I can't download this android game
An error like this usually means the app isn't compatible with the processor in your phone. To spare you the gory details and words like "CPU Architecture" it comes down to the processor in your phone speaking a different machine language than the one the app is written in. This usually means that your phone is either too old, too new, or too weird. Unfortunately this can't be fixed with a software update, the app has to be "compiled" again for your hardware. Knowing what phone or tablet you have might help, but the problem then arrises that you have two or more versions of the app and the user has to know enough about their phone to know what version to download. If the words "CPU Architecture" from before are all greek and swahili to you, then imagine trying to figure out by yourself what version out of five or six options has the correct architecture. This is why app stores like Google Play and F-Droid exist, as they will figure this out for you, but then you have to meet their terms and conditions in order to have your app listed, which may not be worth it for indie or hobby developers.
I reserve the right to be completely wrong, however. Android doesn't like telling the user what the problem is, only that there exists a problem.