Hi Divyansh, You can always try Canva for designing cover arts. It's a really simple tool with beautiful templates. The ideal size for a podcast cover art is 1400*1400 pixels. Hope this helps!
Thankyou so much for reverting I just have one more question: "Is it recommended to have different cover art for each episodes ? "
Hey Divyansh...depends on what kind of branding you wish your Podcast to have. If it has an umbrella topic, then for the same of human psychology having the same cover art works better