I've tried to integrate my blog(hiddenest.dev) to Google Search Console. So, I submitted my sitemap.xml and rss.xml but it failed because of HTTP errors.
However, when I tried to integrate with the origin hashnode blog url(hiddenest.hashnode.dev), it successfully integrated and indexed.
It seems Hashnode refuses Google Search Console bots when the blog uses custom domain.
If that is true, it seems quite critical problem for other users too.