It appears that Tk 8.7a5 on linux has different processing of mouse wheel events from 8.6. On 8.6 and previous, rotating the wheel produces a ButtonPress 4 or 5 event, depending on direction of rotation. This no longer happens in 8.7a5.
Is this an intentional change or a bug?
Is there a list somewhere of changes in 8.7 relative to 8.6?

2022-07-21:
Hi, you can now bind against <MouseWheel> event.
++