Why I can configure my email on Outlook mobile but not on Outlook desktop?

The company’s response says they will not supply you one of their Office licenses. That likely makes sense for them.

If you have your own Office / Outlook license, then explain that to the company and see if they will let you have a Company Outlook profile (which does take an additional license). You already have Mobile access.

If you do not have Office installed on your own computer, you may wish to obtain an Office license. I have been in my own business for years and have my own computer and software to avoid the issue of customer practices and customer software.

If they will not allow you to have a profile for your own desktop, then there is not much else you can do.