I have an unspoken but enforced arrangement when I GM.
If someone misses a session, they get as much experience as the lowest-earning member present. This way no one who shows up with any frequency gets left behind.
The trade off is that when their character reappears we have them either actively in a jam, or just getting out of one.
Ex : Jim had a family engagement and missed last session, where the party traveled to another plane of existence. The next session resumes in this Other Place. The party enters the Field of Blooming Critters and finds Jim’s Thief there, covered in glowing mud, repeatedly stabbing the shuddering just-slain corpse of a werewolf wearing a emerald crown with a shrieking dagger made of intertwined bone and silver. It is up to Jim to explain what just happened and why he is here, or to brush it off with a “Don’t worry about it – good to see you guys again!”
How do you guys and gals handle missing players?