The simpler (and correct) solution in these cases, when you do not want/need wildcard (nor fully automate the process of adding subdomains to the WP installation) but still want the "contents" of a subdomain to load from the domain folder itself is adding an independent "website" (to WordOps/nginx) with the subdomain:
wo site create subdomain.example.com --php74
then remove it's htdocs:
rm -rf /var/www/subdomain.example.com/htdocs
create a symlink to the main domain's htdocs:
ln -s /var/www/example.com/htdocs /var/www/subdomain.example.com/htdocs
and, finally, change the htdocs symlink ownership to www-data:
chown -h www-data: /var/www/subdomain.example.com/htdocs
(do not omit the
: after the username, it is to change symlink group as well).
The "sites" (and all their nginx conf files, SSL, etc) remains handled by WordOps independently.