Are you publishing Sage 300 as part of a session collection that's on the same session hosts that users are RDP'ing into directly?  The performance when accessing a published app vs RDP'ing in should be identical because its doing the same thing, just suppressing the background desktop and using some front end tricks imbedding objects into the local task tray etc.  I have seen some issues through with local machines, especially high-res laptops, doing odd things with DPI scaling that can cause issues.  Doing some research, it looks like there is a bug with the mouse polling rate on certain systems.  Please look at https://learn.microsoft.com/en-us/answers/questions/112989/slowness-on-remoteapps-(windows-server-2019-window and https://serverfault.com/questions/1020864/remoteapp-on-windows-server-2019-lags-heavily as this may resolve your problem.  All of our clients use RDS, Citrix or AVD and I haven't personally run into this one yet, though I'm interested to read up on it as it may affect us in the future.  Best...Tim Townsend.