An anon posted a toggle locomotion controller for 3.0 a month or two ago that let you switch between moving and floating (for sitting in FBT). Unfortunately it didn't work well when used in 3 point so a friend and I have fixed it. Further, you can now set up distinct movement and idle animations for FBT and 3 point/ desktop. DL it here if you're interested
https://cdn.discordapp.com/attachments/677198602279583754/778682871748493322/LocomotionToggle.controller

To set it up:
- Import the controller to your project and plug it into the "base" playable layer in your avatar controller
- DISABLE "force locomotion animations for 6 point tracking"
- Add a 'WalkDisabled' parameter to your list of synced parameters
- Add a toggle in your menu that sets 'WalkDisabled' to 1