As it's behind the monitor it won't be seen so it doesn't matter what it looks like. The monitor's not particularly heavy but adjusting the monitor will impose a shearing or levering force on the join.
See photos attached - as the back is not very flat, smooth or solid, I tried gluing a couple of pads of timber about 7cm square on either side which were linked with a strip of timber to which the bracket was screwed, but they came off.
I guess the key to this is the way the pads are attached. My first effort used epoxy putty to hold the pads on with some hot-melt glue round the edge afterwards but it clearly wasn't enough.