Communists are almost universally against UBI. As much as the right wing wants to portray us as lazy non working people, communists believe that everyone should contribute to society to the extent of their capabilities and should receive at least enough to have their needs covered. Or, as Marx put it, “from each according to their abilities, to each according to their needs”.

UBI is a patch to capitalism. The idea behind it presupposes the existence of unemployment, which communists are fundamentally against. There is no need for unemployment, it’s a fairly new invention (no unemployment in most societies before the industrial revolution), and many nations overcame it (there was no unemployment in the USSR and AFAIK there’s none in Cuba either). Communists want to guarantee to everyone capable of working a decent job, and to people without the physical capabilities to work (due to heavy disabilities, age, or whatever reason) there would be specific aid.

You seem to be missing the fundamental definition. Capitalism is a system where a class of owners exploits those who must sell their labor. A capitalist is a factory owner or a landlord who profits solely from their ownership, not their work. In a socialist state, a worker’s labor has direct social value. They are building a society for all, not generating passive income for a separate class of owners.