@mcolvin @Reddy welcome!
Nextcloud has an external storage plugin - https://docs.nextcloud.com/server/latest/admin_manual/configuration_files/external_storage_configuration_gui.html . With that you can connect S3/CIFS etc. As @mcolvin pointed out, the idea with external storage on nextcloud is that you give access to a bunch of users and they all can store files in this external storage.
If you want to increase the storage space across all users, you have to get so called Block Storage from your VPS provider. For example, if your server is on OVH, https://www.ovhcloud.com/en/public-cloud/block-storage/ is around 5 bucks a month for 100GB. You can attach block storage to Cloudron VPS via http://docs.cloudron.io/volumes and then move nextcloud to that volume via https://docs.cloudron.io/apps/#data-directory .
Finally, if you have massive amount of data, let's say terabytes of data, the cost effective way is to selfhost at home. Attaching a disk at home into a VPS in the cloud is quite complicated and I won't recommend this. The performace will really not be satisfactory.