Description
Bug summary
With any backend I've tested so far (TkAgg / QtAgg / GTK3Agg, installed from conda-forge), beginning a zoom and then press x or y stops input entirely. Pressing a key first before the mouse also prevents the mouse from moving. Once the key is released, the mouse can move again.
Actual outcome
Pressing any key (that doesn't trigger an immediate effect) actually freezes the mouse on Fedora Workstation (tested by me) and Ubuntu (tested by @matthewfeickert); both use GNOME on Wayland.
On Awesome over X, the key/mouse combo works (tested by @tacaswell).
Expected outcome
Zooming with x/y are constrained to the specified direction.
Additional information
If we could find someone running GNOME on X, or KDE on Wayland, we could determine whether this is specific to one or the other.
This also appears to happen in e.g., Firefox or GNOME Text Editor, so it's a general thing, but as you should be able to mix mouse events and keys in games, there should be a way somewhere to enable that. But if not, we may have to change constraints to use real modifier keys, i.e., shift/ctrl/alt.