Real estate people I have a question; How does Redfin place an estimate on a house that’s no longer on the market?

Not a licensed realtor but ...

An estimate is just that..... an estimate (or guess).

They typically base it on what other similar houses in the immediate area have sold for..... condition be damned

In other words .... it is just a guess when they say "estimate", but it gives you a good ballpark figure when adding or subtracting for "condition"

IE: They "estimated" a house down the street at 300K, but it sold to an investor for 175K as it had holes in the drywall everywhere and the basement was flooded from a pipe break...

they look at what places close to and similar in size/features have been selling for and throw in a little secret sauce extrapolation.
e.g. if a house in a nearby neighborhood that has the same number of bedrooms sold last week for $300, but your house in a district with better schools... and more/better/easier public transit they estimate it to be... well. close, usually.