This is incredibly vague, but it was some point and click sort of game with Mickey Mouse in it that was on Windows 98.
This is a long shot but was it Walt Disney World Explorer?
Don't think so. It didn't involve Disneyland in any way as far as I can remember.
It sounds like Mickey Saves the Day. I still own it, but haven't played it for years so my recollection of it is probably as vague as yours. I'm pretty sure it ran on Windows 98.
Nope, not it.
I realized it would probably just be easier to Google it, so I did. I couldn't find what I remembered when I searched for Win98 games with Mickey. Turns out it was a DOS game, not originally for Windows 98, oops.
I thought I played it in a Windows 98 PC, but my memory about it was super vague. One thing I did remember was something about a xylophone.
It was
Mickey's ABCs: A Day at the Fair for MS-DOS