They sent out an update due to overload on servers or something that you have to open files in browser or client in order to edit and cannot do so inside Teams for now. You can open in browser or client from the top right button while document is open or from the ... next to file before opening.
Same here. We have an E2 license and several of my users are having the same issue. I have one user who can edit Word but can't edit Excel spreadsheet. I have another user who can't edit anything in Teams at all.