Depends a bit what is on your nextcloud.conf. The one from the documentation?
https://docs.nextcloud.com/server/16/admin_manual/installation/source_installation.html#apache-web-server-configuration
If you use this, I’m not sure if perhaps something in the .htaccess gets in the way.
However, I’d consider to use a separate subdomain. For security, it’s the host prefix:
and for the configuration, having two different virtual hosts is much easier to deal with (have different configurations, move certain vhosts to different machines, …) and usually don’t cost anything. For configuration, you can use cname records so you only have to keep one entry updated with your IP.