My window cleaner does ours. He has teleosopic Tool that has camera attached and high pressure water supply and verious other tools that connect to a very powerful vac. It really does a very good job. Oncce gutters are cleand of debris they are then washed out with foam brush and vaced dry. The soffits and facia are then cleaned. Well worth the £ 70.00 he charges.
I’ve seen a few specialist gutter cleaners locally that use a large vac that can go over a conservatory or extension, they have a camera on the head so you can see what’s going on in the gutter.
Enyaq EV