Same. We've got the high calorie Boost and he's been managing 2 a day but that's still only 1/3 of the calories he's been told to consume to maintain weight. (It's available on Amazon, by the way. Hopefully that helps so no fruitless searching happens for you). Found some recommendations for Boost Soothe on the Head and Neck Cancer subreddit as it's created for cancer patients with oral discomfort. Supposed to be just slightly thicker than water, clear, and I'm hoping he can turn to that when trying to eat to swallow down food. 300 calories per 8 oz.

Meanwhile MIL made greek stuffed veg that burned his mouth so... I guess I know who will be eating that for the next however many days. I can hear the scale screaming in fear already.