I went through this last year.
Your new Windows system does not have an installed, licensed copy of MS Office. Try and reload the old copy from CD/DVD and see if Win 11 will even allow it.
In my case I had to log into my MS Office 365 account and manage the desktops where I have my Office registered to. Good luck if you can’t remember that account name and password.
MS is trying to move all Windows users over to a model where you pay by the month for using their software. They get monthly revenue, you don’t really need to worry too much about upgrades, but you never own any software and pay for it forever.
I would start the move over to Libre Office or Open Office, if you can’t find the old copy of Office or are not allowed to reload it.
Just wait until you get told that you really do not own your Windows 11. It’s coming.
I do have a full copy of Office 2016 that I got from an employee offer at work. I had that installed, but I upgraded it to Office 365 for the full OneDrive terabyte of space.
-PJ
Yes, https://www.libreoffice.org/ should be the solution for deoetdoctrinae. If you want my basic homemade tutorial (written for a Christian interested in making graphic signs) for it then I will upload it. Also change file attributes. May we use all for God and good.