These strips originally ran in October 1989. While Garfield is never funny, these were are intentionally not humorous. These rather dark comics puts Garfield in a position of loneliness and starvation.
Some of theorized that Garfield actually is dieing in these strips and that every strip after this is just delusions of his mind. As pointed out in the last strip Garfield’s only defense against starvation and loneliness is “denial”.
Of course the most likely scenario is that this just a nightmare Garfield is having and he wakes up at the end and lives his life happily. It has been said that Garfield creator Jim Davis had just had someone close to him die and he wrote these as sort of a self therapy.
Official Garfield Website