-Where do you save your files? Do you save to a network?
I saved it in my computer
-Is some automatic process running (at nicht: backups) or anything?
i think not
-Any crashes when saving the files?
none
-Are there third party plugins?
All elements on the drawing were made on ilustraitor except the picture I uploaded to draw above it
-Which version of Illustrator?
version 2021
-Can you analyze the file with the layers panel - is there a clipping mask or has everything turned into pixels?
I'm not sure what do you mean with analize, but in Layers now is just one layer, the drawing kept the quality, just some elements moved a little.
-What happens when you turn off "Save in background" in the preferences? This will not fix existing files, this is only for files you save in the future.
is that option in the 'File' tab?
Thank you for the answers.
In the layers panel you can look inside the layer. You just need to click on the little triangle to see what's there. I don't think it has all been merged into one object. It might be slightly less editable, but that depends on what exactly you created. If it's a clipping mask, then you can release it.
The Preferences are in Edit > Preferences and then "File handling" for the "Save in background". This is for the future, it won't affect existing files.
But I would re-save the file you are having trouble with by doing File > Save as and then check the necessary options.