The first thing I noticed here is that the textbox doesn't have the usual context menu with commands like "Select all" and various IME features. It's not clear whether RTL and bidirectional capabilities are there, and if so, how to use them.

Next I clicked on the combo box, it opens the dropdown, and I try to use arrow keys to navigate it. That doesn't work. Is that because I opened it using the mouse? Nope, still doesn't work if you tab through the widgets and use Enter to open. Looking up items by typing the first few characters doesn't work, either.

This is all really basic stuff that native widgets offer to any app for free on any platform.