How to find a cloud service with functionality like a NAS like Synology or Qnap? Is there something like a personal account for clients to exchange files with them?

Question

NAS

Our company uses NAS to share files with our clients. Each client gets an account (login, password), with which he can connect to the NAS and upload the necessary documents. We also post our documents for each client. It turns out something like a personal account for each client. Those. we have access to all documents of clients, and clients only to their own.
NAS, of course, is good, but something faster is needed and, preferably, with the ability to display some information for the client in this account.
Naturally, the level of customization should be simple and understandable for an advanced user.

Answer 1

Hetzner recently launched Nextcloud, for example.
https://www.hetzner.com/storage/nextcloud

Answer 2

https://nextcloud.com/ will work?

Answer 3

Corporate rates from Googledrive or probably the same dropbox