OptiPlex 7020, Dual VESA Mount, monitor drops to the lowest position

We purchased the Dell OptiPlex 7020 series, and I have a borrowed DELL OptiPlex Micro and Thin Client DUAL VESA mount with Adapter bracket . After mounting this bracket onto a DELL monitor, the monitor does not hold its height/tilt, and under the weight of the OptiPlex and adapter, it drops to the lowest position.

I have tested multiple DELL monitor models (U2412, U2415, S2722DC, U2715H), and they all behave the same way. Is there a list of compatible DELL monitors where this mount can be used without the monitor changing its height/tilt on its own? Ideally, I am looking for a 27" WQHD model.

Please be advise,
thank you

PS: Of course, I can use an external monitor stand with a VESA mount, but I would like to use the original Dell

monitor stand.