Hi @Thanasis Stikas
Is your Office 2019 a retail version?
If it is a retail version, it's recommended to log in to: Setup Office - Office 365 Redemption or https://www.office.com/setup, try to bind Office license to your Microsoft account.
For more, please refer to: To redeem a new purchase in Where to enter your Office product key.
After binding your Microsoft account with the Office license, you can download and install it directly from the Subscriptions page.
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