If you’re at a point where you’re genuinely having trouble getting the calories, add some easy “dirty” ones aka tasty ones.
As to the peanut butter shake, my once go to in a similar situation was:
2 cups whole milk, 1/3 (maybe1/2?) cup steel cut oats, few scoops of
Peanut butter and a scoop of protein powder blended really good in a quality blender. It was roughly ~1,000 calories and went down easy.
Also no shame in using sauces. That boring chicken breast can gain 200 calories easy with some chikfilet sauce. That rice slides down easy with some olive oil.