Clearly the problem is that the word "Acquiring" or "Acquisition" never appears in the PowerPlay system info on Galaxy Map on the right side. Many other words and visual noise appear (Unoccupied, multiple other statuses like Fortified, Undermining, Stronghold, etc) but never Acquiring / Acquisition.
The filter appears to work, but the filter is hidden in a tiny icon on left-side Power Play in Galaxy Map. If you filter by Acquiring then click any resulting systems you will still never see the word or label "Acquiring" anywhere for the system's info. Also the filter keeps resetting to default instead of resuming whatever choice the player previously did, when of course the player will generally be looking for their own allied power.