Wait for application launch without using Thread.Sleep() using FLAUI

I am new to using FLAUI and Automation Testing and would like to use it to test my system. At the moment I am using a Thread.Sleep() to wait till the application launches to then find the Login textbox. Is there a more efficient way to do this rather than using Thread.Sleep()?

At the moment i launch the application and use Thread.sleep(10000) to wait until the applicationis fully launched and that the logIn textbox is find-able before clicking on the control to input the password to enter the application. However I understand that Thread.Sleep is the worst way to tell the system to wait especially in automated tests. Could anyone offer any other things i could test out?