Solution or IT service sought for storing hybrid data from highly specialized systems

I am looking for a solution for a doctor's office for the audit-proof and space-saving archiving of entries in highly specialized encrypted “database systems” with text entries via PDF files, image and video files, and data in proprietary file formats. There are varying numbers of new entries per data record at irregular intervals.

I am therefore looking for a local, daily, audit-proof storage solution for hybrid data from a highly specialized system. An IT service may also be an option. The data must be stored on our server.

It is essential that

a) there is at least one base file,

b) changes are backed up daily (no real-time archiving necessary), and

c) it is NOT a cloud solution.

For practical reasons, it makes sense if storage requires little time and the data volume is as small as possible (e.g., similar to how mpeg works).

I am initially looking for a solution that works for a very small company and is therefore inexpensive. If the provider is able to initially expand this to approx. 410-820 users within a reasonable period of time (approx. 2 years) and at a reasonable cost, this would be a bonus.

(Note: If it is not possible to map every change to an extensive database, a pure change log would also be acceptable).

One central server (1-2) is planned for each software workstation. Work is carried out in an MS Windows system landscape.