You may receive a "Couldn't Fetch" error in the Status field for your sitemap, even if your site was already crawled.
This error may occur if you submitted your sitemap URL incorrectly. Check to see that the URL path in the sitemap field on the left does indeed say "/sitemap.xml" and not the page URL (e.g., "/homepage"). If it was submitted incorrectly, go ahead and submit it again.
If the sitemap URL is correct, please note that this error is known to occur for sites hosted with any company, and is not related to Wix. In most cases, it resolves itself within a couple of days or weeks. However you can submit the URL using the Inspection Tool to speed up the process.
You can also try adding a new sitemap with the name '/sitemap.xml/', and refreshing Google Search Console. This will fetch your other sitemaps, and you can delete the newly added sitemap afterwards.
This article is credited to the Wix team - https://support.wix.com/ and we thank them for that!