Here's a quick breakdown of the key differences between SharePoint Server and SharePoint Online:

SharePoint Server vs SharePoint Online

Feature

SharePoint Server

SharePoint Online

Hosting

On-premises; your organization manages the servers

Cloud-based; Microsoft manages the infrastructure

Management

Full control over hardware, software, and updates

Microsoft handles updates, patching, and maintenance

Cost

Higher upfront capital expenditure (hardware, licenses)

Subscription-based; predictable monthly or annual costs

Scalability

Requires manual scaling of infrastructure

Highly scalable; resources can be adjusted as needed

Accessibility

Accessible within your network (can be extended)

Accessible from anywhere with an internet connection

Updates

You control when and how updates are applied

Microsoft automatically applies updates

Customization

Extensive customization options

Some limitations on deep-level customizations

Maintenance

Your IT team is responsible for all maintenance

Microsoft handles infrastructure maintenance

More in detailed: https://www.shoviv.com/blog/sharepoint-vs-sharepoint-online-a-detailed-comparison/
In simple terms:

  • SharePoint Server is like having your own in-house file server and collaboration platform. You have complete control but also the responsibility for everything.

  • SharePoint Online is like renting space in a large, managed office building. Microsoft takes care of the building's upkeep, and you can focus on using the space.

The best choice for your organization depends on your specific needs, resources, and IT strategy.
Solution for you:

  1. SharePoint Migration tool
  2. Backup SharePoint Online
  3. Migrate SharePoint Site to another Tenant