Encryption Key Rights

Can you use the same encryption key from two different computers?  And is there an issue with using the encryption key with Microsoft 365?  

Yes, you can share the encryption key to be used in a different computer. And not, you can not use the key with Microsoft 365, since some of the features like downloading submissions as Excel files are not available: https://www.jotform.com/help/344-Encrypted-Forms-and-How-to-Use-Them