Rabbits who are unneutered are very difficult to bond to others (both rabbits, other animals and sometimes even humans). The hormones will often cause unpleasant behaviour like humping/mounting, agression and territorial behaviours. Some people whose rabbit can’t be neutered give their rabbit a stuffed animal and lots of toys. This doesn’t satisfy the need for interaction, but it may serve as a distraction (and ahem… “companionship” in case of the stuffy toy).
Before resorting to that it’s best to verify with your vet that there really is no possibility to have your rabbit neutered. There can be very valid medical reasons that’ll leave a rabbit unable to be neutered. However, neutering will also prevent many medical issues. Rabbits are prone to hormonal cancers, especially for females it’s very important to be neutered. Sources vary, but the chance of an unspayed female developing uterine cancer is high: 50-80%. While males can get problems too, they’re more prone to unwanted behaviours, stress and extreme frustration. I’d discuss this further with a rabbit-savvy vet to make a plan together.