Well, there are workarounds for your issue, You can open an image file [loading screen image], maximize that image and bring it to the front using the invoke message. Or using parallel activity you can open a browser where you can load a loading screen gif.
Looking for UIpath material from basics! Refer to this video on UIpath provided by Intellipaat:
This was as far as displaying a page is concerned, if your concern is user input disorienting process, you can block the user input using commands.
If you are asking as a developer to help you understand if the process is running or not, a good tell is Ui-Robot icon which appears in the system notification in the bottom right-hand side corner in a windows environment or you can hover over the UiPath Studio icon in the app tray it’ll either display a green play button indicating there are no automation currently running or a red square will appear indicating there’s a process currently running