If one has an issue using store.kde.org, there seems no obvious way to report issues in something remotely appearing as a serious issue reporting system, as used from elsewhere.
The only thing I found is https://store.kde.org/contact which sinply gives an email address. While I had success some time ago when I once tried that email address, it still feels not reliable, as usuallly such contact addresses are associated with email nirvana.
Also in case of issues there is no shared ticket/issue history where one can see what already got reported and what state the issue handling is in.
E.g. the creator of https://store.kde.org/p/998798, obnosim, seems to have a problem uploading a new file: "In the Files tab during the product editing process. I select a file, a progress bar goes up to 100%, then nothing happens.".
I would have no idea where to point the person to report their problem and have it looked at by an store admin.