Hi Júlia,
Big Sur 11.2.1 was installed in my macbook pro last week
We are on 11.2.3 now.
Just a few questions, but first double check how many Photo library's you have.
1) Does the photo app actually open?
2) Do you mean if you open the photo app it just crashes?
3) Does open but you see no images?
I would double check preferences as my first screen shot.
and make sure you library is selected as my second screen shot, to do this hold down the alt key while opening the photos app.