This might be a stupid problem but so far I dont know how to solve it.
When I try to copy my downloaded soundfonts to /boot/system/data/synth it says that I am not allowed to copy because the volume is read-only.
All advice how to solve this would be mostly appreciated.
There was a bit of shuffling around of directories wit the update to package management.
Most of /boot/system is now read-only and can be used only with packages (in hpkg format). But, you can use /boot/system/non-packaged/data/synth.
I didn’t check if the midi synth is looking there, if that doesn’t work, please open a bug report.