The only thing that changed affecting the UI is we introduced UI themes, but by default it is disabled unless you enable it as shown in this video.

I'm not sure if that is the issue or something else.  You would need to contact the vendor of TestComplete as they understand better how their tool works, and we would be happy to collaborate with their product engineers so they understand what changes they may need to make to ensure continued compatibility.  They can directly reach our product management by emailing product@appeon.com.

Alternatively, you may want to consider AscentialTest.  The vendor works closely with our engineering team to ensure their tool supports every new version of PowerBuilder.  And to the best of my knowledge, no other testing tool on the market can test PowerBuilder objects (especially DataWindow) as thoroughly as AscentialTest.