I don’t really use a specific software, I just put a part in roblox and take a screenshot with a green screen, then edit the green part out. It seems to work fine for me.
Just use whatever you think provides the best results
You could draw something in 3D style, do the method @yourcomputerhasdied said, take a photo and edit it, etc. As for programs to do that, I have no clue but as for the methods all of this works depending on the game you are making.
You can use blender and photoshop model the item in blender and color the item in blender get a good angle then take a screenshot then in photoshop if you don’t own photoshop use photopea. You don’t have to edit the image in photopea you can use any other software I just recommend photopea or photoshop.