Go to Settings>Storage and add the path to the folder with your FLACs
If you don’t want your Apples in Roon you can disable the Music folder as I have.
I may have misunderstood what you’re trying to accomplish when making my first response.
If your ALAC and FLAC files are located beneath the same folder I don’t think there’s a way to have Roon not see the ALACs.
But I’m not certain. Someone else may know.
So you could use the Focus feature to hide ALAC when searching for music but the ALACs would still play in Roon Radio.
I too have some music I don’t wish to have in Roon.
I keep it in a separate folder and only have Roon Storage setup to watch the folder with the music I care about.
My drive looks like this.
Only the folder named “Roon” is setup in my storage settings.
If it really bugs you that the ALAC files are in Roon and they are mixed up in the same folder as FLAC, try opening Windows Explorer (I’m guessing your core is on Windows but you didn’t say) and make sure to sort by “File type” and select that column so the folder is organized by type.
Then select all those ALAC files which should be in order in Explorer, and drag those ALAC files to a completely different folder that Roon does not watch.
If you’re paranoid about file loss and you have the hard drive space you could copy them to a “safe” folder before dragging.
If you’re a Mac user you’d do the same in Finder (EDIT: I see you’re using a MacBook. So Finder it is)
You shouldn’t need to nuke anything in Roon database. It wouldn’t be a bad idea to shut the roon server application before moving any files
If you don’t want to move files or somehow can’t, Focus will help you filter them out when sorting.