I've distributed/uploaded the IPA via XCode to appstoreconnect.apple.com and I can see that my latest version is under "processing". Since this is not a "new/fresh" app on appstoreconnect, it seems like it's not required to have a new screenshots and the app submission is instantly under processing status?
If I wish to update the screenshots, wondering if there is such option for me? Or is the option yet to be available due to the reason where it's still under "processing" status? And may I know usually how long is it gonna be under "processing" status?
You need to update the screenshots before submitting for review, as apple will need to review screenshots with every app update, if your App status is processing for App Store it means it got approved and you already released it and soon it will change to Ready for Sale. So you need to wait for next build submission and make sure to update screenshots before submitting for Review
Note:
The above is for app status, if the build is showing processing
it means you just uploaded from xCode and it will take some time to be able to select that build, after that you will be able to update screenshots and release notes and finally submit for review