General consensus is that running helps with your cycling, but cycling does not do much for your running.
Personally, as someone who was forced to train on a bike for many years the transfer was not much, and some of it was negative.
What cycling (and swimming) did was get my 5k down from like ~24 minutes from just jogging 1-2x a week to 20:30. But even as a fit cyclist, my HR would be totally maxed out while running, legs would hurt, etc. I had no running strength and no aerobic fitness for running. I still had natural speed, but that's just talent/neuromuscular strength.
I had a resting HR in the low-mid 40s but would max out at 200+ at 6:30/mile pace during a 5k. Zero efficiency/economy.
All the biking also led to overdeveloped quads, so in running I had no hip strength and was sitting back a lot when I fatigued. Currently working a lot with deep squats and deadlifts to improve the posterior chain that got weak during all the sitting and cycling.
Lastly, cycling also falsified lactate tests in running, assuming a higher fitness than I actually had (my cardiovascular system was well developed, but running muscles weren't so I got oxygen deprived quickly). This also led to me training too intense in running which turned me into a lactate machine (very fast kick/high lactate tolerance but bad threshold/stamina).
Sadly, my engine is not that big so any sport is tough for me, but I respond very well to training so I can become a quite decent cycling and also runner.
With a big engine, I'm sure I could be a good cyclist and runner, swimmer only if I would start training it early (unfortunately in Europe kids are still being taught the breaststroke only and not freestyle in school which is super silly).