Stop foobar2000 from grouping together MP3 and FLAC files on the album list

You could simply add %codec% to your view pattern.

For example:
In Preferences: Media Library > Album List, create a new view called "by artist/codec" and use the following pattern:

%<artist>%|%album%|%codec%|[[%discnumber%.]%tracknumber%. ][%track artist% - ]%title%

(The pipe | characters make it a separate level in the tree hierarchy.)


File > Preferences > Media Library > Restrict to: > "*.FLAC" (copy/paste without the ")

or

File > Preferences > Media Library > Exclude: > "*.CUE; *.MP3; *.M3U" (copy/paste without the ")