I downloaded version 10.0.0 to see if they had added this again in later versions like 10.7.0. I created a new project, used the input box and I can still use the "Show as password" option Can you show a screen shot of your application?
I checked now, and in Mendix 10.7.0, it works the same way as it did in Mendix 9.24. Could you please elaborate on what exactly you mean?
Below is a screenshot of the text box property from mendix 10.7.0