Heres my current PrusaSlicer Profile for the Geeetech Thunder.
Check the Start G-Code at the end, theres a K-Faktor, u may need to adjust it!
Also i fixed the BMG Bowden Coupler with this one: https://www.printables.com/de/model/53861-improved-tapered-thread-bowden-coupling-pc4-m6/files
Why? becaus eof this Issue: https://www.youtube.com/shorts/pILKWtlzL7A
Here is an YT Short from the Fix: https://youtube.com/shorts/d5_O6qkf_-Q