Nope, I also got to that point and got stuck the same way.
My guess is that
- either the map is incorrectly built by the game developer (with some unpassable terrain there)
- or the game developer has placed that invisible wall on purpose to prevent progress till the next version (like restricting that boss battle to patreons or maybe blocking a bug/glitch he needs to fix but did not have the time before release.
Btw. did you know that there is another CG event that becomes available only after triggering the event in the ball room?
You have to trigger the ball room event but do not need to find Deiarothi.
The map -> Leave Rest Point to the right and then go down to the exit on the lower left there to get to "Rest Point Forest Inner":
View attachment 4659149