I concur with this, there are contributors to this forum who plainly never proof read their written thoughts before posting.
Proofread is one word. Honestly, it's like reading The Guardian in here sometimes...
I use the traditional spelling - two separate words - "proof read" - which then over time became a hypenated compound noun - "proof-read", then finally a closed spelling, as one word - "proofread". All are correct.
Similarly "today" started life as "to day" in Middle English times, then for several hundred years became "to-day" as evidenced from historical writings and manuscripts, finally becoming the modern, closed spelling we know "today"
None of which you'd be likely to find in The Grauniad, famous as it is for piss-poor spelling!