Difficulty ending straight line tool

[Ofnuts]

1. move to end point
   
2. depress Shift (shows the straight line) (you can still move the end point)
   
3. with Shift stilll depressed, click to draw
   

Repeat from 2) for connected straight lines (polygon).

There is no "draw" mode, the pencil is always active until you switch to another tool.

PS: Gimp 2.10 is over 2 years old, why are you still on 2.8?