If you’re going with 2D graphics and you’re not an artist then my biggest recommendation is for you to make your own - but keep them simple. Some of the most impressive indie games I’ve played have had really primitive graphics but they’ve used their limitations to make a distinctive style - whether that means going with vector lines, crude pixel art, simple geometric shapes or even ASCII art. Just find a style you can produce quickly without it getting in the way of development. I shouldn’t need to recommend any specific 2D art software to you, there’s tons out there.
If you really don’t want to make your own art, steal it! There are a ton of sites with sprite rips of classic 2D games. You can’t make a career on stolen game sprites but no one is going to be sending you legal threats for you making your first few simple games that way.