I know you probably mean road cyclists, but I haven't seen Trailforks mentioned. Nothing beats it for singletrack route planning.

Komoot is good too, but at least in my area of NA the elevation calculation is off by quite a bit. When I've used it for longer routes, I've ended up putting in at least 1,000 ft more of climbing than it has told me would be on the route. Trailforks doesn't have that problem.

If you have a local IMBA chapter, most of them have accurate trail profiles as well.

For road cycling routes, I use Strava. If you want detailed routes that are popular with local cycling clubs, Trek stores usually have surprisingly good handouts on local routes.