Games

I would say older than that (well maybe not elite), as much as the tech could handle it you should include:

https://en.wikipedia.org/wiki/Turbo_Esprit

Here you had several town maps, including dual carriageways, main roads, side roads, one way streets. And you could just drive down any of them. They were all nondescript, but the amount of memory really limited what could be done.

There was also the games using the freescape engine. Driller, Darkside and Total Eclipse. These were all about as open world as you could achieve on the hardware of the time.

In terms of "open world" the definition is open to interpretation. I'd argue that text based adventures were open world too in their own way. So it really depends on what features people agree makes an "open world" game as to what the first game that contains all those features was.