A popular device to increase Dec rigitity.
I have been using this bracing technique since the mid 60's when I used to build long focal length Newtonian reflectors for planetary/lunar imaging.
Also known as a Hargreaves Strut after an English amateur astronomer, this simple bracing strut can make a big difference to the rigidity of a system where the mount is small in relation to the length of the telescopes.
If the telescope assembly is a permanent setup, the use of universal joints is overkill, however, it does allow for ease of fitting and adjustments.
I have one set of universal joints and a selection of extension rods (thick walled tubing is more rigid than solid bar), which I interchange with several mount/telescopes combinations.
The brace is fixed top & bottom and simply rotates with the scope in RA.
In these images I have extended the dec dovetail with aluminium section to give me a much greater triangulation & rigidity.