Yea currently OBS-Studio can only output to one stream provider, so using a server like nginx to send it to more than one place would be an option. You can also use a service like restream.io if your upload is limited for example. You stream to restream and they send the stream to the services you want.
Last but not least, as BeardyBro mentioned, you can run OBS more than once but will run into problems capturing applications twice or a webcam more than once for example. In the future it is planned to support more than one output location directly within OBS. Not sure how far up on the priority list this feature is though. So it might take some more time until this feature gets added.