Same problem on MS Access 2019 since a short time. This is obviously a BUG in one of the following Microsoft updates:
The reason is that in the event handler: Private Sub Form_MouseWheel(ByVal Page As Boolean, ByVal Count As Long), the 'Count' value is now always zero. See https://answers.microsoft.com/en-us/msoffice/forum/all/mousewheel-event-no-longer-working/cf536228-e259-4358-ae74-fd6d26b4e2d4?rtAction=1736865225831. Hopefully Microsoft will correct the bug soon, but meanwhile I would be grateful to anybody proposing a solution to work around the bug (can Count be read by other means ?).