Hello, @eflchina

Yes you can install NextCloud on the same droplet. You can host multiple websites on one droplet by adding multiple Virtual Hosts. You just need to create additional virtual host for another domain name or install NextCloud in a subfolder so you can access it as you mentioned in your example: example.com/nextcloud

If you’re using Apache you can check this tutorial:

https://www.digitalocean.com/community/tutorials/how-to-set-up-apache-virtual-hosts-on-ubuntu-18-04

And for Nginx you can check:

https://www.digitalocean.com/community/tutorials/how-to-install-nginx-on-ubuntu-18-04

Step 5 – Setting Up Server Blocks (Recommended) it’s the one you need.

You can also check this tutorial which is still valid and should help you as well - https://www.digitalocean.com/community/tutorials/how-to-set-up-nginx-server-blocks-virtual-hosts-on-ubuntu-16-04

Hope this helps!

Regards,
Alex