Start with a spreadsheet and enter numbers 1 to 9 in a column and mark them. Goto menu Format > Conditional Formatting > Condition. You get the "Conditional Formatting" dialog with focus on the "Add" button.
Try to reach the area of "Condition 1" for to set your values. That is not possible without mouse.
Use mouse to select option "between" in the middle drop-down list. Now try to reach the two input fields right of it without mouse. It is not possible.
Tab does not work and none of the dialog elements has a label with underlined character to use Alt+character to set focus.
I can confirm with Version: 18.104.22.168.alpha0+
Build ID: 3d30a39ee92678f6a4e71bd450fc044636adedab
CPU threads: 4; OS: Linux 4.4; UI render: default; VCL: gtk3;
*** This bug has been marked as a duplicate of bug 115040 ***