There's no way to select multiple items in the tree view when on a modern Linux distribution. Shift-clicking and control-clicking don't do anything.
This seems to be the same bug as mentioned in this post: https://esotericsoftware.com/forum/d/26784-ctrl--click-to-select-multiple-elements-not-working-on-manjarolinux
In that post, the OP logged in using an X11 session instead of a Wayland session and this solved their problem. I can confirm that logging in with an X11 session, this bug doesn't occur. It only occurs in a Wayland session. However, this bug will affect almost all Linux users, because Wayland is either their distribution's default session, or their distribution is planning on adopting Wayland and deprecating X11.
Using X11 also disables several useful features of my computer, like setting my display scale to 150% or using touchpad gestures. It also runs slower. As a result, it would be a real pain to have to use an X11 session to work in Spine, especially since X11 is being deprecated and might not be safe to continue using.
Steps to reproduce
- Open Spine 4.2.40 in Fedora.
- Import a PSD into a new project
- Click on one slot
- Hold down shift and click on another slot
Expected outcome
The range of layers inbetween the first and last slots are all selected
Actual outcome
Only the slot which was last clicked on is selected. See screen recording:
Current workaround
At the login screen, when entering your password, choose "GNOME on XOrg" from the cog menu in the bottom-right menu. This logs in using an X11 session instead of the default Wayland session, but this creates its own problems like no fractional scaling, no touchpad gestures, and reduced computer performance.
I haven't tried to reproduce this bug on Ubuntu, but I suspect it would occur there as well.