Orbi RBK50 speed locked at 100M

Ok, based on your screenshot, it looks like you're getting a gigabit connetion between the Orbi router (RBR50) and your modem (which would be the WAN connection), and only 100 Mbps over the wired LAN to a device (computer?). Since the Orbi has gigabit ports for both the RBR50 and RBS50, for all ports, both WAN and LAN, it's probably the case that whatever device you have connected by ethernet to your RBR50 only has 100 Mbps capability. This may be a technical limitation of the NIC, or a software setting in the device, or, potentially, a cabling issue, where the devices (the Orbi and your computer or whatever is connected) both have gigabit capability, and both have it enabled, but your cable is either not capable, or is damaged, and so the best they're able to autonegotiate is 100 Mbps.

Start by checking the capability of the attached device and make sure it both has gigabit ethernet, and that it's enabled in the settings. If yes to both, then try replacing the cable. For testing purposes, you could use the cable you have connecting the modem to your router, since that's already showing 1,000 Mbps. You may just need to replace the cable you're using.

Also, to be clear, your screenshot shows the RBR50, which is the router (and only the router has a WAN port anyway), but your post talks about a device connected to the satellite (the RBS50). But, regardless, all the ports on both the router ans satellite are gigabit ethernet, so it's either the attached device's NIC, the NIC settings, or the cable used to connect the device to whichever Orbi device you're referring to.