There isn’t I’m afraid (for the usual reason that cycle.travel isn’t really able to support routing options), but as of the latest update, c.t does try and avoid infrequent ferries if the frequency data is recorded in OpenStreetMap. Unfortunately with the Brixham ones it looks like it isn’t – if you’re familiar with editing OSM you can edit the data yourself, or if you just drop the information in here I can have a go.

(Separately it looks like c.t seems to like the ferries more in gravel mode, which is curious – I’ll take a look at that.)