Is Quickbooks Desktop Pro 2020 available in Mauritius? Because when I click on buy, there are only 2 supported countries (US and Canada)

You may consider QB Online Global version for Mauritius

https://quickbooks.grsm.io/Africa

Should you prefer using QB Desktop, company only offers US, UK, and CA version. If you don't need any specific requirement, I would recommend QBD US version instead. You may purchase a one time license with a lower price thru a partner/reseller.