Edit: the starting, blank page (with the plus icon in the bottom) made me think the app failed to load. Some guidance for a first-time user would be great.
Also, those buttons on the bottom right are a UX anti-pattern, in my opinion. They're hard to notice, and it's not always clear exactly what they do. On a larger screen, they're a tiny footnote on the bottom right side of the page that is hard to notice.
I will add some text to show in case of empty list. I agree the button (FAB) is difficult to find on large screens but it is part of the Material design guidelines (https://material.io/guidelines/components/buttons-floating-a...). I will think of some other approach.
You can decide to blindly follow standards or do some real user testing and see how well your UI works for people. Stand over someone's shoulder while they use it for the first time and see how quickly they figure it out. Do some A/B testing.
For the record, the UX/UI community in general had a lot of negative reactions to Material when it was introduced:
https://medium.com/tech-in-asia/material-design-why-the-floa...
https://medium.freecodecamp.com/material-design-and-the-myst...