You can switch by using the desktop version of QuickBooks, @pavlos-gabaeridi. The program allows you to manage multiple company files with a single one time license. Let me provide further details about this.
QuickBooks Online (QBO) and QuickBooks Desktop (QBDT) are two different platforms. With QBO, you can handle one company profile per subscription. This means you'll have to sign up for one account per company. While QBDT will let you create as many separate files you want using a single license.
Since you want to manage multiple company files with a single one time license, you can consider using the QBDT US version. You'll have to first download, install, and activate the program into your computer. Once done, that's the time to import your data to QBDT. Just make sure to back up your file for future use.
After you create a company file, you can start using QuickBooks right away. However, you still have to continue setting up your business to make sure your financial statements are accurate. To learn more about this, you can check out this US article: Get started with QuickBooks Desktop. It includes helpful links to perform each of your tasks in completing your company setup.
Please let me know if you have other concerns. I'm just around to help. Take care always.