A question was asked within the Robot Framework community. That is "Does anyone know how to interact with ... mat-select fields in the robot?". This is a detailed response that delves into both the specific problem but also some themes around that question and my examples.
I have alot to say (why these locators, what is this Angular Library and a lot of how one uses it, etc) but little time. So I expect this to be a incomplete and conssistanly in flux gist. But hopefully it is helpful.