I actually decide with the players one of 3 methods for missing players after I got sick of trying to come up with ways that they pop in and out every session. A. Your character was assumed present but invisible, you get filled in and were there in character B. Your character ceases to exist, there is no in-story explanation and you’ll need to catch up on the details in character. C. The missing player comes up with a reason for their disappearance and what they were doing
But I’ve also had some fun with it before, One of my players in high school warned me ahead of time that once school started up again they’d not be able to make it until the next break. This resulted in them being possessed by the BBEG and culminated in the party saving them as the break started up again, I then had the perfect excuse of them being partially processed by the defeated BBEG who was taunting them with their past, so when they missed a session it was because of possession or manipulation by said character.
I’ve also heard of people having some on-the-nose solutions like getting whisked away to another dimension to help them defeat an evil villain between sessions or getting lost in a pocket dimension/ethereal plane.
I’ve managed to talk 3 people to death, I love bards