Needed to serve an html file at siteurl/zohoverify/verifyforzoho.html in order to verify domain for zoho mail.
Problem is: NextJS uses routes without extensions
You can just put html files inside /public and Next will serve them according to the file structure.
Seems that when Next is matching a route, it first checks /public and then dynamic routes (/app dir).
If you want to keep html files in /public/html, take a look at the next rewrite docs