Dell Inspiron
Windows 10
Office 2016.

Help! We have a home Dell PC with Windows 10 and Office 2016. We have two user accounts created on the machine.

User 1 has a situation where Office files cannot be opened from File Explorer. Double-clicking on the file causes File Explorer to turn faint, and the mouse cursor becomes a spinning circle. File Explorer hangs and has to be killed. Lather, rinse, repeat. Right-clicking on the file engenders the same response. Non-Office file types open normally.

User 1 can work around this by first opening the Office application (Word, Excel, PPT) and then using the interface inside the application to open the file. Even choosing "Browse" from within the application and opening a File Explorer works. Double-clicking or right-clicking from within THAT File Explorer works as expected.

User 2 has none of these issues. Everything works as expected.

This has evaded my best efforts at debugging, and has been going on for weeks.
User 1 is very patient, but this is ridiculous. Could this be some conflict with Microsoft Online (which I detest and may have tried to neuter)? Do I need to just reinstall Windows and Office? Please help!