Unity bug or what?

Hi everyone, I'm new in unity. I'm using version 2019.3.0a7 and I'm creating a top down 2d game. Everything seems ok, but after a few seconds, in the scene view and in the game view, nothing is seen anymore. If I start the game (ctrl + p) it returns to normal. It also happens when I open external programs, like browsers, and then go back to unity. here are some pictures( I put the link because unity gives me the parsing error when I try to load an image.):

1) when I open unity https://i.postimg.cc/mZF7z5yz/Immagine.png

2) after a few seconds (or if I open external programs) https://i.postimg.cc/9QvhMzmq/Immagine1.png

3) after a few seconds it gets worse again https://i.postimg.cc/bvQKwTVK/Immagine2.png

4) if you start the game you can see it well https://i.postimg.cc/1tXcjRFJ/Immagine3.png

5) if I press ctrl + p again to stop the game and return to the scene view everything returns to normal. https://i.postimg.cc/mZF7z5yz/Immagine.png

the problem seems to be only in the scene view and in the game view until I start the game. Is it a unity bug or did I set any parameters wrong?