Hi,
I have the old Bogen/Manfrotto hexagonal quick release plates on everything. And, only one tripod and one monopod which work with those plates. Usually, I use the things in the landscape orientation, but sometimes the tripod head gets rotated into portrait. The QR system is secure enough that this never worried me, much less was ever a problem.
The medium format camera I've had have two tripod sockets, one for each orientation, so that was nice. I just needed an extra QR plate.
Enter the new (to me) Fujifilm GFX-100. I was wondering about that before it arrived. No second tripod socket for a second QR plate, and a heavy enugh rig where I wasn't all that happy with the idea of rotating the camera and lens sideways like I do the smaller format cameras.
But, wait. There are L-brackets like some have shown here. Just use one of those. So, I took one of my old school QR plates and bolted an Arca clamp to it and there we are. The screw clamps the jaws to secure the L-bracket. It has enough surface area to hold the bracket with no tendency to slide sideways. And, for portrait orientation, I just loosen the clamp and turn the camera and tighten the clamp.
What's nice here is I don't have to convert anything else over. Just release the old style plate and I'm back to where I came from.
Stan