All the GUI tools won't work.
Just now I found myself in the situation to split some old FLAC/WAV/CUE combinations I created as a backup for failing CDs, back in the day. I remember that XLD should be up to the task of splitting them into separate files but for reasons unknown it did not work. No matter, that's what the shell is for.
On macOS, install via Homebrew:
brew install cuetools shntool flac
Run this for FLAC files:
cuebreakpoints file.cue | shnsplit -o flac file.flac
Run this for WAV files:
cuebreakpoints file.cue | shnsplit file.wav
Then import and tag with beets and you're done.