Folksongs are accessible to everyone. They are like national parks, public works, beaches etc.
When a written song is proclaimed as a folk song, chances
are, it isn't. The folk process works against copyright laws that rewards a single claimant for "intellectual property". No one owns a folk song.

It's important to separate the folksong from the folksinger. The folksong emanates from a sub-culture ie:
Appalachian, Blues, work-related groups like cowboys, coal miners, prisoners on chain gangs etc.

A folksong undergoes changes and becomes a "variant".
Maude Irving's "I'll Twine Midst the Ringlets" from England becomes A.P. Carter's "Wildwood Flower" in America.
The folksong changes to adapt to a new environment.

There are songwriters who make "folklike" songs, that is,
songs that are in the style of traditional folk songs.
Tom Paxton, Phil Ochs, Woody Guthrie, Dylan......

When a folklike song surfaces it is often confused with the
authentic folksong. "Over the Rainbow" may yet become a folksong (which would not make Yip Harburg happy) because
it will undergo changes that adapt to new conditions.
(Barbara Allen will find herself walking the highway home instead of a cowpath.)

Rock and Roll is a record company designation and not a folksong one. The labels are often produced after the music is created. Pop music is written for the marketplace. Folk music is preserved for the public trust
or if you like "the Commons", (a term that will not please
Libertarians.)

If a song survives and becomes more significant than its author/composer than it is likely a folksong. If it reflects the values of a cultural subgroup, then it is likely a folksong.

You can't write a song and automatically call it a folksong. If a song falls in the forest and no one
is there to listen, is it a folksong? Nahhh!

The term "folksong" itself is a designated one redefined by
the musical marketplace to sell recordings to a target audience. This doesn't invalidate the folksong origin.

Again, it has to be accessible so that anyone can learn it,
sing it, use it without financial penalties or having to deal with its author/composer/publisher.

A pop songwriter or even a topical songwriter can write a folksong if it becomes 1. changed, 2. survives generations,
3. renounces ownership of intellectual property.

Frank Hamilton