Solved Can't edit CSS/SCSS

Should be a local problem. I have no issues editing and saving either css or scss.

ha well it's not local I tested on live sites and locally on wamp server and
when testing with kunena version 6.2.3 it still works just fine
so 6.2.6 too and with version 6.3.0 it suddenly goes wrong

By local I mean server configuration or browser (cache?).
And the latest version of Kunena is 6.3.1! So no use testing on older versions.
But can confirm this happens with Joomla 4.4.5.

Added to github .

Thanks for reporting to Github.
But to be clear, I don't have a cache browser cache or server misconfiguration.
I just have a live site with joomla 4.4. 4 and kunena 6.2. 6
worked first updated to joomla 4.4. 5 and also updated all extensions Kunena 6.2. 6 edit template custom.css still worked fine
after that I updated the Kunena version to version 6.3. 1
and checked with kunena tools Diagnosis no error messages
but after that update the problem is clearly present
can no longer edit the kunena template custom.css and custom.scss

So this is a Kunena bug which needs to be fixed Kunena-side?

Yes, i have just made the fix for it : github.com/Kunena/Kunena-Forum/commit/3d...530425b1f95e6fabdb98