Hey Kenney I really like you public domain work, today i bought kenney Studio but unfortunately it doesnt works on my mac 10.11.6 and kenney studio NXT is far from prefect and not good yet.
Unfortunately Mac OSX has updated some of their requirements which means that older software doesn't work anymore, having to update the older versions of the software means less time to fix and work on Kenney Studio NXT. Kenney Studio NXT is being worked on and will soon have all the features that the previous versions had.
Played with kenney studio on windows and that was amazing, i hope new updates of NXT version make it amazing too specialy ability to make animations
also i want to know is it ok to create sprites with your tools and upload them in opengameart or other services ?
Yes! The animation support will be amazing, I'm having great fun with an early version myself. Yes, you can use/distribute the sprites you've made in any way you want.