I had a liver and kidney transplant about 6 weeks ago and I can completely relate to this. At first I could hardly eat anything but I forced myself to get something down. I had no appetite and it still isn’t much better. Things don’t taste the way they should. I think that he will find that it does slowly get better. Give him time and talk to your transplant team about any concerns. The strong meds that we are on also bring some side effects.
As to being ‘spacey’ I find that I was very much so but it is getting better with time. Best of luck to both of you.