It’s likely the part is locked. This is what the Flux documentation says:
“Locking an Object
There are three ways of locking an object:
- Object tree: go the "Objects" tab on the left, find the target component and click on the lock icon
- Context menu: right-click on the target object and select "Lock"
- Hotkey: Use Shift+L
What is Disabled?
Locking disables the following interactions on the PCB editor:
Drag
Context menu and hotkeys for:
Add
Delete
Disable
Rotate
Flip layer
Align
Space Evenly
Trace Width
Replace”
If you see a lock icon next to the item in the Objects panel, unlock it there, then try Delete again.