An official statement from the European Commission on accessibility "overlays" and EAA compliance. The outcome? Overlays are insufficient and potentially damaging to accessibility. Whilst they don't go as far as to actively state "do not use" or "considered harmful" both conclusions are supported by their statements:

Claims that a website can be made fully compliant without manual intervention are not realistic, since no automated tool can cover all the WCAG 2.1 level A and AA criteria. It is even less realistic to expect to detect automatically the additional EN 301549 criteria.

In other words, overlay tools may make a website less accessible for some users.