Hi @RareSloth,

Did you try to click+drag and hold a mouse for a second? The box selection should appear. Dopesheet view - Spine User Guide: Box selection
We made a box selection disappear when you release the mouse button quickly. This is due to the workflow for the users with the stylus. In the 4.1.10 beta you can choose to have this option on or off in your settings, depending on your work preferences. Let us know if it works.
Thanks!