Here's how to draw nice smooth lines in GIMP. It doesn't matter if you are using a graphics tablet, or a mouse.
In GIMP choose the Brush Tool.
In the Tool Options, choose the following settings - making sure you set the Smooth Stroke options.
GIMP's smoothing works by using a Weight and Quality setting, which causes a slight delay between the cursor and stroke, alowing you to smooth out little jitters caused by using a stylus or a mouse. If you think the effect is too much, you can reduce the quality and weight sliders until you get the optimum behaviour.
Even a small amount of smoothing with much lower Weight and Quality settings will make a huge difference, and reduce the delay to virtually nothing. Compare smoothing switched off (on the left), and switched on (on the right).
On further investigation of your image file, I can't actually replicate the problem with GIMP and my cheap Wacom Bamboo tablet, even with Smoothing switched off, so I guess something else is wrong. Perhaps the graphics tablet drivers?
This example is with GIMP 2.10.2 - Wacom Bamboo, with Brush Dynamics: Pressure Size turned on, and Smoothing switched off.