I am able to disable a second monitor and stick with one screen.
However I can't use DisplayFusion (manually or via profiles) to re-enable that screen.

Some insane flickering happens for a few secs and then I get the error message "Failed to call SetDisplayConfig. [HR: 31]" forcing me to switch back to only one monitor enabled.

Is this a known issue? How can I make it work inside DisplayFusion?
Turnaround I found was re-enable it on Nvidia CPanel then re-apply the DF profiles.

Setup:
Windows 11
Software v9.9 (Steam)
RTX 3070
1 - DELL S2722DGM on DP @1440p 165hz
2 - ASUS VG278 on DP @1080p 165hz
Both w/ GSYNC active (Dell is not certified, while ASUS is)

Yes
When I disable it is under option "only on monitor 1"
then I change back to "extend to both monitors" and it works.

There you go

Was this issue resolved? I am seein the same error and experiencing this. My guess is maybe some issues with identifying the monitor when off?

FYI, this exact thing has happened to me for the 5+ years I've been using DF, I've just never taken the time to submit a forum post about it. I can't believe I found this article 6 days after your message about a backend updating happening soon. Here is hoping!!