RDS - How relevant?

For all intents and purposes, RDS has remained unchanged in Windows Server 2019/2022. Microsoft's focus is on Azure Virtual Desktop, and it's unlikely that RDS will see meaningful changes in future LTSC versions of Windows Server. The company's answer for customers that want to host virtual desktop infrastructure (VDI) on-premises is Azure Virtual Desktop deployed on Azure Stack HCI, currently in public preview.

It's important to note that Remote Desktop Modern Infrastructure (RDmi), originally previewed in late 2017, was intended to be the long-due update to RDS. However, the technology of RDmi was instead used as the basis of Azure Virtual Desktop (originally announced as Windows Virtual Desktop in late 2018.) Given that their previous effort at modernizing RDS turned into a hosted service, I think it's unlikely that they will put any further effort into RDS other than security, bug fixes, and compatibility.

Azure Virtual Desktop (and Windows 365) are Microsoft's focuses for virtual desktop infrastructure. Those services are where new features and capabilities will be delivered, like it or not, and are where you should look for your long-term planning.

Similarly, as Harm_Veenstra noted, Microsoft is making it very difficult to support Office running on Windows Server (such as in a Windows Server hosted terminal server or session-based desktop environment). If you're using the Office 365 apps, they will no longer be supported on Windows Server after late 2025. If you're using the perpetual (LTSC) versions of Office, it get more complicated depending on what (if any) Office 365 services you're using.

In VDI environments, Microsoft is using a combination of licensing benefits and Office end-of-support to push users away for session-based Windows Server desktops to the multi-session versions of Windows 10 and Windows 11 - which, unsurprisingly, can only be licensed for use with Azure Virtual Desktop.