Since the latest update the six sample faces are blank. I can still select one and change complications, but can't see what I'm doing. This is on an Apple iPhone 12
Does it work if you go to the Garmin Connect web page from your browser? You should be able to access it from here:
Or if not, from the main page here:
login, then tap the watch icon on the upper right, select "Device Settings" and you should see the six sample faces. Perhaps not as convenient as doing it from the app, but it could be a temporary workaround until Garmin fix this.