It could either be an oldham coupling. The photo's a bit blurry. Here's a web page on oldham couplings. https://www.huco.com/products/couplings/oldham-couplings
or it could be a Flexible flange coupling
Could you not make a guide of sort to constrain the plunger action on the load cell to be along the right axis. Something like that (probably can do something better, but that's all I had time to do):
so fairly tight around the diameter of the pin (say 5.5mm hole), and resting on the surfaces of the load cell to ensure perpendicularity. Can the plunger move ...
That might be overkill in your application (but I don't know).
Figure 1. A random rigid flange coupling from an image search.
A rigid flange coupling may be a more economic choice if it suits.
From the comments:
What are the benefits of a rigid flange compared to a split flange beside costs? Doesn't the flexible coupler give more friction?
A flexible ...
I am going to say that no, your chosen coupling would not work. Based on the K-K cross-section in the drawing, there would be a large portion of the shaft that is not in contact with the coupling.
I believe what you need is a coupling where it is held against a flat in the shaft by a set screw, like the one here (though in your size): https://www.omc-...
There is one pin in each shaft, so each pin takes the full load but in two places. This is known as double shear.
If you put 2 pins for each shaft then there would be 4 sections of pin taking the load so the pins would need re-sizing, otherwise they would be too strong and something else more expensive will break.
There are dozens of ways to connect to the shaft of a motor, A few examples:
set screw/grub screw
through taper pin
keyway & key (most common industrial use)
Each of these has a torque spec that I think you can find in a mechanical engineer's handbook. There are probably decades old free ones on the ...
These drive clutches can be used to absorb drive train shocks and/or slight mis-alignments of the two shafts.
These are available in several sizes and capacities.
Flexible coupling or flexible drive coupling or flexible shaft couplings, see:
enter link description here