Macbook Opening Up Excel With Windows of All Files From My Desktop

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H0urglass wrote:

and then all of the apps on my desktop (Excel and other file types) open up on Excel with messages coming up about converting or not converting files, saving or not saving workbooks (again of the wrong original format) starting with bootmgr file opening.

This part is concerning since "bootmgr" is a Windows specific file used for booting a Windows system. I haven't worked at that level on a Windows PC for some years so I forget if that file is a text based file or a binary executable file. I don't know why anyone would have such a named file on their Mac even if it was not actually the Windows "bootmgr" file I'm referencing.....very odd name for someone to use if it is not that Windows file.

We did a Cloud Transfer instead of through wires and double checked everything was correct before wiping the old one.

I hope you had/have actual backups as well and did not just rely on iCloud as a backup solution. iCloud is not a backup for macOS even though iCloud is a backup option for an iPhone/iOS. And an old system should not be erased until the user has thoroughly tested the new system. As you can see after using your new Mac some more that something is wrong...not enough testing was done prior to erasing the old system. Without any backups, that old system would be a useful crutch in case a mistake is made trying to fix the new system.

People should have frequent and regular backups of their computer and all external media (including the cloud) which contains important & unique data. There are a lot more new ways to permanently lose access to the data stored on the internal SSD of recent Macs due to all of the hardware, software, and security changes.