These are the two which I heard are perfect fit for the Ninja 650 Stem hole. Haven't tried them myself due to the Illogical pricing.

https://www.amazon.com/Mounts-Lab-Motorcycle-Compatible-ML-Ninja01/dp/B09VGQPGFG

https://www.amazon.de/-/en/gp/product/B00M0T1WTM/ref=ox_sc_act_title_2?smid=A3PT4HPCTKFK3C&psc=1

Mounts Lab MotoMount Ninja-... https://www.amazon.com/dp/B09VGQPGFG?ref=ppx_pop_mob_ap_share

I used this with the ball adapter and vibration dampener on my 2017 650, and it works great and is very solid

Pulling on it lifts the front of the bike up.