I'm also a Komoot subscriber. You are correct Komoot includes many routes created by other people but it is also one of the best route planning system especially for Europe including the British Isles. Say, I am in Co. Donegal Ireland and know the e-bike Rental is located in Carrick F94 VY84. I intend to see the famous Slieve League cliffs. Opening Komoot, entering the postal code and now just five practical routes for a Road Bike show up. I just select one of them, and that's the one and only that allows seeing what I want to see. Splendid! However, Komoot is even better for route planning if there are more alternatives, and you need your own route. What is great for Komoot is it takes the Bike Type in consideration. Wanna MTB, Gravel, Road, Touring? Click and here you are! Komoot will select only the appropriate surfaces, and will warn you against many surprises en route (stairs?)
It's good when riding roads and cycle paths, where much of this data comes from official sources too. But it has flaws elsewhere - especially if you ride off-road (Singletrack/woodlands/gravel etc), where it's often using user-contributed data. (To OSM or Komoot).
Especially in the UK. We have Rights of Way (footpaths, bridleways, byways etc) and Freedom to Roam laws (open/common land), often across privately owned land. Exercising your rights doesn't mean you won't encounter objecting landowners. They might make it as difficult as possible. (Thankfully many don't!).
For example. Just on my last ride, it tried to navigate me up a Bridalway. The bridleway was signposted - so was legit, but it meant going through a farm yard, with the farmhouse adjacent and machinery all around. The farm gates were closed. It felt too much like trespassing on private land to open those gates, ride through the middle of the farmyard and look for this bridleway, which wasn't obvious from the roadside, so I ultimately had to ride around it. But someone must have made it through at some point, so the data exists. In reality, it wasn't a good route.
This isn't the first time it's done that ever. Recently I was directed to a footpath at the end of someone's garden. You had to ride down their driveway, behind the house and to the rear of their garden to find this footpath. Again I didn't feel comfortable following the route and diverted around it.
I could give many more examples. The only blessing is people report these segments on Komoot/OSM so they're either removed or warnings like you've posted above are added.
So while it's good, and I've subscribed, I have to say it's not 100% reliable. User-contributed data has its faults and it is best to review the routes.