The stock saddles on cruisers are usually not great for long rides. I changed the one on mine to a Brooks B67 saddle that is just perfect for my cruiser and supremely comfortable.
I’d also look at the grips and pedals to see if they can be improved. The pedals on my cruiser caused me discomfort after about 15 minutes of riding until I swapped them out for Shimano Saint MX80 pedals that are much more comfortable.
Having said that, a cruiser is never going to be a long distance machine.