It’s possible in Mendix, but you need less readable logic:
In my opinion it’s better to create a Java Action and use the WordUtils library with capitalize() or capitalizeFully(). Examples are available here: https://examples.javacodegeeks.com/core-java/apache/commons/lang3/capitalize-words-of-a-string/
You can call the Java Action in an OnChange microflow or just before your save action.
You can add an ‘on leave’ or ‘on change’ event on the input field to trigger a microflow. In the microflow you can change the member with the toUppercase() function in combination with substring().
So for example if you want to change the word ‘hello’ to your specifications you would do the following:
toUppercase(substring($variable,0,1)) + substring($variable,1)
Also see: https://docs.mendix.com/refguide/string-function-calls