We have friends who took a Danube River cruise years ago. Going in, they didn’t now that the boat constantly put them ashore to take a bus to the next place where they could re-board the boat. It was awful.
It all depends on when you go. In 2019, we took a Viking cruise from Budapest to Amsterdam. We noticed that earlier in the year the cruises were a lot cheaper, and also later in the year.
Turns out that in the spring, the snow melting raises the river level so much that the cruise ships can’t get under the bridges, and in the Fall, the river levels drop due to the normal drought conditions, so the rivers are too low for the cruise ships to navigate.
We went the first of May and had no problems.