From: #4509 (comment)

This is a long-standing known issue on (the default configuration of) some Linux Window Managers, where they completely took the Alt key for manipulating the window (why they didn't choose the Win/Super key, or use that key now, is something intriguing for me... a little upsetting I'd say).

• I'm not sure if it will be possible, but we might be able to detect the Alt+click issue for some window managers (hard coding the detection for every possible window manager that did this "very smart" decision).
• Probably a generic solution where a mouse drag event when Alt key is pressed and the window is being dragged (by the WM).
• We could show a link to a solution like: ALT Key doesn't work with (Quick) tool shortcuts on Linux #1621 (comment)
  or other options (like changing the Alt with Win/Super key for the eyedropper inside Aseprite).

Reported several times:

• ALT Key doesn't work with (Quick) tool shortcuts on Linux #1621
• Alt to use Eyedropper does not work (but regular eyedropper does) #4405
• Eyedropper Tool (quick) not working on Aseprite v1.3.7 on Linux Mint 21.3 #4509
• https://steamcommunity.com/app/431730/discussions/0/2970649384341291248/
• https://elk.zone/mastodon.art/@playmedusa@mastodon.gamedev.place/112551717620340146
• etc.