I’ve struggled with appetite issues for a while now and my go-to whenever I can’t get myself to eat regular food is nutritional drinks like Soylent, Boost etc. Enough calories to replace a meal and you won’t miss out on nutrients.
Name brand ones are unfortunately super expensive so I usually stick to the Kroger Fortify+. I know you said flavor isn’t a priority, but avoid vanilla. It’s wretched. Chocolate is the one that’s most palatable.