Since a few versions ago Matomo uses TEMPORARY TABLEs to store some data during archiving. As these tables are temporary and only have one column, they don’t need an index for performance and therefore have no primary key. This works fine for most users, but it seems you (and a few other people) have set up the Database server to refuse to create any table without a primary key, which therefore breaks this part of Matomo.
As there are more people with such a database setup, a fix is being developed in the last few days:
It would be great if you could report back if this works for you.