Very good solution from @taylorclark, thank you very much.
If many more products without attributes are imported, as it happens to @thsingh, it can be a problem with the cvs file, at least this way it happened to me, at the end I ended up editing the cvs in open office.
Another thing that happened to me is that when I changed the values of Attribute # global to “1”, when I imported it, I lost the variations of the products in woocommerce and I got a printfun alert about this. What I did to solve this and it worked, was at the end of the cvs I duplicated the columns that belong to each existing attribute and their values (Attribute # name, Attribute # value(s), Attribute # visible, Attribute # global, Attribute # default), then placing another consecutive “#” in the identifier in each of the columns of the new attribute, then I can create duplicates of existing attributes in the product, in those duplicates is where I changed the values of the column “Attribute # global” to “1”.
When I imported the cvs back into woocommerce of course I have those duplicate attributes, but by keeping the custom ones the product variations are kept.
The new duplicate attributes created are not used in the variations, nor do I make them visible in woocommerce (uncheck options), but they are used in the filters in the store, and in Printfun there are no alerts. I hope it can be useful to someone.