iTunes has changed its requirements for uploading podcast images from RSS feeds. Docs offer a range of options but request largest size which is 3000x3000
Size: Square; 3000 x 3000 pixels. If you’re submitting your show via RSS feed, Apple Podcasts accepts show cover artwork ranging from 1400 x 1400 to 3000 x 3000 pixels. The largest size is preferred.
iTunes has changed its requirements for uploading podcast images from RSS feeds. Docs offer a range of options but request largest size which is 3000x3000
https://podcasters.apple.com/support/896-artwork-requirements#:~:text=Size%3A%20Square%3B%203000%20x%203000,to%203000%20x%203000%20pixels.