Unless the disc is burned as a data CD containing MP3 files, then they are supposed to be audio CDs containing lossless PCM data (almost literally WAV). This is definitely the case unless the MP3 is converted to WAV then burned as an audio CD.
If you want to store the audio from an audio CD losslessly, then there are no benefits in choosing WAV over FLAC. That is just wasting storage, since a FLAC will store the WAV without any loss.
If you don't mind changing some bits resulting in a lossy but virtually indistinguishable-from-the-original quality, then use a modern lossy codec like Opus (or even AAC or even Vorbis). That way, you save a ton of space without affecting the sound quality, assuming you chose a high enough bitrate setting.