More directly:
Create 2 profiles in OBS, one for each of your streaming services. Name them accordingly "Twitch" and "Youtube" or whatever you're using.
- switch to one profile, then configure server and stream key for that service
- Switch to the other profile, then configure server and stream key for the other service
Now you are able to switch services by switching profiles without the need to enter the stream key each time.
Profiles store their own copy of audio and video settings, so if you want the same customized settings, it's wise to not create a new profile (which has all default) but instead copy your current profile for the other streaming service profile. But once you have multiple profiles, configuration changes you make in one doesn't reflect in the others. That's the intention of profiles: often, you need different resolution or bandwidth settings across streaming services.
However, scenes and sources are shared between profiles.