I understand, and listen there are fantastic short books like Of Mice and Men, The Houseguest: And Other Stories, or even more abstract like Grief is the Thing with Feathers, BUT I think a great way to get back into reading and get the stamina back in check is a good middle-grade fiction book!
Super easy, often a race to the finish, couple twists, fun characters, and lots of whimsy before adults think they are too old for whimsy.
Some options I would recommend to start are Magnolia Wu Unfolds It All, Matilda, Hatchet, The Alchemist, The Secret Garden or even a Percy Jackson!
It’s important to remember reading is fun so starting with a fun book is a great trick!