SSMS 19 opening new files in another instance

Hello,

After upgrading to SSMS 19 (uninstalled all other versions), the annoying thing is that the app keeps opening multiple instances of the program whenever I open a new file.

How can I prevent this and have all files open in the same instance (as it happened in SSMS 18)?

This is so annoying and unexpected from a company like MS. 

Thanks.