The walking bass is a type of bass line that follows the chord progression by outlining the chords. Walking bass lines are generally played as one quarter note per beat (four per bar), root note on beat 1 of each bar, and leading note on beat 4 into the next root note. These are the characteristics that make a bass line "walking."

Variation in rhythm can happen as long as the main feel of the bass line keeps the steady one quarter note per beat rhythm "walking" feel. How often the chords change depends on the style. There is music that has lots of chord changes where you'll hear the chords generally change on beats 1 and 3. In this song, there is repetition in the bass line, especially in the verse that carries over to the chorus.

https://youtu.be/WydAn6jWH00