I have a very elderly dog (border collie mix), who is on her last legs. She is getting pretty weak, lost 20% or more of body weight, doesn't seem to have a whole lot of joy in life, but doesn't seem to be in pain, can walk and perform waste excretion functions more or less normally. She has months to go at best.
It's like "the chicken or the egg". We don't know if her appetite is poor because she's weak, or if she's weak because she's not eating enough. (She also has a mass of unknown type in her abdomen, vet isn't sure, and doesn't think it makes any sense to pursue diagnosis or surgery). At any rate, it seems like it'd be good to persuade her to eat more.
We have tried many things. And she'll like something for a few days or a week, and then turn her nose up at it until we discover something else. Bread seems the most reliable, especially sourdough and crackers. And of course she eats better when hand-fed. So we seek advice on general strategies or specific foods. Obviously long-term healthfulness of diet is of little importance, e.g. we've considered feeding her (non-chocolate) ice cream, but apparently too much dairy can be bad.