On this song written by George Harrison, McCartney played a bass line as usual (on his new Rickenbacker bass) and then overdubbed another bass running through a fuzz pedal. Here are both of those lines (regular on left, fuzz on right).
For the regular bass line on the left, Rob is playing a 1985 Rickenbacker 4003 (red) strung with LaBella flatwound strings. For the fuzz bass line on the right, he's playing a 2022 4003S (maple) strung with Rotosound roundwound strings. Both basses are going through a SansAmp VT Bass Deluxe.