What a shame for both of you, Nana56 - you should be having a lot of fun in your free time as well as enjoying separate interests and time spent with others.
If his retirement coincided with the pandemic, I can see why he might feel down and possibly a bit cheated. Life has changed dramatically for everyone, hasn't it.
Unless he has some physical ailments, it does sound as if he is depressed. He really needs - if you have a surgery that does actually see patients - to visit his GP for a check up. He may well resist that idea, feeling depressed and disinterested. Maybe you can contact the Doctor instead and explain that you are very worried about his attitude - he shouldn't be apathetic and sitting in a chair most of the day; nor should he be objecting to your going out and about if he doesn't want to go with you. If you feel guilty, then you will end up pleasing nobody - least of all yourself, unless you take some action very soon. With less enjoyable weather coming, there will also be a further excuse for him to avoid going out and about. Does he have friends? Would he be likely to respond positively if you encouraged someone he likes to contact him and suggest an outing? Don't despair but don't just leave it and tailor your life to suit one that really doesn't work for you.
Get some help, hopefully the Doctor will persuade him to come in - even for some small health check! Then he can judge for himself whether your DH would benefit from a possible short course of "happy pills", or something to help him see that life can and should be fun as a newly-retired chap.
Good luck and make sure you keep up your own interests and me-time!