score:3
You can be pretty confident that they'll run the service they currently say - National Rail Enquiries for 27/07/22 midday shows the strike timetable
That's a major route that will be prioritised for the short operating hours. They seem to be planning to operate most services in the middle of the day on that route, comparing tomorrow to Thursday, though at slightly shifted times.
Having said that, I don't plan to trust them as I'd be getting the penultimate or even the last train to Bristol from Cardiff and don't have a plan B.
Live departure boards for the next 2 hours are found via https://www.nationalrail.co.uk/times_fares/ldb.aspx
Specifically for your journey, you can bookmark: from King's Cross to Cambridge and from St Pancras to Cambridge - they're adjacent and served by the same tube station but have different services.
In the recent strikes, at least on the South Wales line, they did manage to stick to their greatly reduced timetable, with fairly normal delays.