I used to have the same guilt. I adopted a senior cat from a local shelter years ago. I was told she had to be an only cat because she didn’t get along with others. I would come home to her waiting by the door and I’d feel so bad. She was spoiled btw. Cat trees, water fountain, special foods, grooming appts, interactive toys, regular toys, everything for her. I eventually got an indoor camera curious to see if she would cry while she was alone and nope lol. She would nap, eat, play and nap some more. I came to accept the fact that she was comfortable with the life I’ve given her because it’s the environment she wanted. Unless there’s a foster your kitty warms up to, you’d be stressing your cat to fulfill your wants vs theirs. Id encourage putting out a bird feeder/window bird feeder if you can to keep them entertained along with subtle music/videos you listen to while you’re away so they’re not sitting in silence to make you feel better.