If you'd like to use multiple RTMP streams, you can accomplish this with OBS using a plugin.
obs-multi-rtmp is a plugin for streaming to multiple RTMP servers concurrently.
This plugin is able to share encoders with the main output of OBS to save CPU power. It can also use standalone encoders with basic configuration (bitrate).
The current release comes with multiple language translations.
The source code can be found here.
Steps to install the plugin
1. Download the latest release from https://github.com/sorayuki/obs-multi-rtmp/releases/
2. Unzip the zip file into the OBS folder(located by default in C:\Program Files\obs studio).
3. Open the below folder path
4. Complete the installation
NOTE: Minimum requirements for this plugin are OBS-Studio version 26.1.1 or later, OBS-Studio main unit version built with QT 5.15.2.