That's another extreme and just wrong. Of course if you were a dissident or just had wrong friends you couldn't even publish a cookbook, but plenty of non-members of either the party or the writers union were publishing their stuff, see Kir Bulychev as a notorious example or an ordinary guy with the disdain for the party (and his father was a lawyer thrown out of the party and his grandfather fought in the White Army, so he was certainly "на карандаше") who nevertheless was one of the most popular Soviet science fiction writers. Or Genrikh Altov (known to some HN users for his TRIZ) who was a political prisoner and had a conflict with the union.
So yeah, it was possible. Before 1987 your stuff had to pass the editorial board and литование by the censorship body, and of course you must not have been viewed as disloyal or suspicious. Travelers, beginner writers, critics, etc. all published their stuff. I have a 1982 fungi reference book written in Ukrainian by a non-member of either the union or the party, just a long-time amateur outdoorsman.
In any case, games were freely published. Magazines in particular routinely published listings sent by random readers.
It's not really publishing as a private person. Which was impossible/illegal as people didn't have access to printing equipment. Yes you could publish it by sending it to a newspaper or magazine.
My dad had a bunch of samizdat books and periodicals. Some were typed on a typewriter, some were printed on a dot matrix printer (closest to what you can call directly accessible mass printing in the USSR). None of those were recipe books, these were all texts impossible to publish.