After receiving my Nikon Z9 I was in need of an L bracket but was initially forced to use a generic camera plate until the Manufactures started to produce custom L-Brackets.
The wait is over and you have a few choices:
The Kirk L-Bracket features a modular design allowing you to remove the L part of the bracket if not needed or if you find it too much of a hassle to use with cables out in the field. The Kirk L-Bracket for the Nikon Z9 is a very solid design comprised of stainless hardware and milled anodized aluminum. An Allen tool is affixed to the bottom that can be used to tighten the bracket to the camera and or of course remove the bracket. The retail cost as of this Bracket is around $195.00. You can find yours at B&H Photo, Video, and Audio store.
The Kirk L bracket is well made and durable that is geared for the photographer that requires a secure way to mount their camera to an Arca Swiss head. The bracket has two stainless screws that help prevent the camera from falling to the ground if the swiss plate is slightly lessened.
If you simply need an L Bracket for your Z9 for general photography using a Tripod for Portrait or Landscapes - I highly recommend the Kirk L-Bracket.
Other Option: The Kirk Plate lacks the robust accessory connections of the SmallRig solution for the Nikon Z9. The SmallRig offers the same high quality with attachment points for lights and monitors. The SmallRig solution is a better choice for videographers that have Audio and other accessories. Get your SmallRig using my Amazon Associate Links.