Unofficially, yes. Stop Roon. Move the Roon database directory to another drive. Use “mklink /j” to create a junction reparse point from the original location to wherever you moved the Roon database folder to.
The OP was specifically asking about moving Roon’s internal metadata database to a location not on their boot drive. They were not asking about the raw music files, themselves. Roon already lets you have music anywhere you want it. Only the metadata database has a hardcoded path.
and ended up with what seems two identical …\Roon\Database folders on 2 different drives. Roon is importing, the target directory is growing in size, but available space is still decreasing on C:\
Is this expected behaviour?
You have the arguments reversed, so you created a junction from F:\Roon\Database that points at the C: drive. You can confirm this by doing a ‘dir’ in a command prompt in F:\Roon. It should show “Database” as type JUNCTION.
So you will need to stop Roon again, delete F:\Roon\Database, again move the origin to F:\Roon\Database (since Roon has been updating the C:\ drive), then run mklink /j with the correct order. Confirm that the C: drive “Database” shows as type JUNCTION. Then restart Roon again.