Burying the vocals in the mix dominated the early R.E.M. records in the 1980s. It didn't mean that the listener couldn't make out any words in the murk. Indeed, words and even phrases could be interpreted but there were always passages when you simply could not make out what they were saying. And, back then, there was no internet to quickly search out lyrics. It also ensured that you often had no idea what the song was about, which in some cases may have been for the better.
This is Hyena from Life's Rich Pageant (1986). Have fun with the lyrics.
And from the same album, These Days.
One of their earliest tunes, Pretty Persuasion from Reckoning (1984).
My personal favorite, Driver 8 from Fables Of The Reconstruction (1985) which does have a partially intelligible lyric:
The walls are built up, stone by stone,
The fields divided one by one
I saw a treehouse on the outskirts of the farm
The power lines have floaters so the airplanes won't get snagged