Obviously, the husband is one of the main characters as the title is centered around him. There must also be the person who is responsible for 'leveling him up', perhaps the wife or a close friend.
One key theme could be personal growth. As the title implies, 'leveling up' the husband might involve his development in various aspects like character, skills or status. Another theme could be relationship evolution. The process of 'leveling up' is likely to have a significant impact on the relationship between the husband and the other characters in the novel, perhaps leading to a stronger bond or a new dynamic.
I'm not sure specifically as I haven't read it in detail. But generally, it might be about a woman's journey to enhance or improve her husband in every possible way, perhaps in terms of his skills, personality, or social status.
It could be a romantic comedy genre. The idea of 'leveling' a husband has a touch of humor to it, and if there are relationship elements involved between the husband and wife, it may fall into this category.
I don't know for sure since I haven't read the novel, but I assume the main characters would be the wife who is on the mission of levelling up her husband and the husband himself.
Since I don't know the exact plot of 'leveling my husband to the max novel', it could be that the story is about a woman who has a plan to transform her husband into the best version of himself. This might involve various challenges and comical situations as she tries different methods to 'level him up', perhaps in his career, relationships or personal growth.
You might consider giving him some space to explore the manga on his own and then discussing it together. Sharing your enthusiasm and showing how it brings you joy could potentially get him on your side.