Hi

>>>> after several problems with autocad you were able to solve the problem.
Did you solve all problems with installing new AutoCAD version or with reinstalling an old one?

>>>>>However the drawing files appear to me with an icon different from the one I had a year ago (i.e. it showed me the preview).
Do you mean the way how they show in Finder? If yes, then this could be of Finder's "View options" settings.
Can you attach screenshot of what you see?

>>>>many files in .tmp format what are they for?
Do you save your drawings in a folder with iCloud sync enabled? Can you show screenshot of this issue?