It’s only the top 1% of European companies that have more than 50 employees, for the majority it’s not the need for scaling enterprise solutions that is the problem. Something like Linux + LibreOffice + Nextcloud + EU e-mail/hosting/backup providers could in theory work as a replacement for big-tech.
The first major issue is going to be the price, I seriously doubt you are going to be able to match the price and quality of the Google and Microsoft products.
The second issue is going to be business specific application, that only are available for Windows.