Hi,
As normal use if covered for RDS too, with your E3 license you are allowed to install your license on up to 5 devices with the user you hare where the license is assigned to.
Im not a license expert, but that is from mind what I have of understanding of it.
According to a Microsoft document (https://go.microsoft.com/fwlink/?linkid=2139145&clcid=0x809&culture=en-gb&country=gb), shared computer activation is permitted for Microsoft 365 apps in RDS environments just to confirm that too. Hope it helps.