Just not realistic anymore to achieve these days imo. It hasn't been done since Pantani in 1998 (questionable) and before that it were the true greats like Indurain, Hinault and Merckx who did it. If I'm not mistaken, all of Contador, Nibali, Froome, ... have tried and failed in the last decade or so.
There's just over a month between the end of the Giro and the start of the Tour (this year even less than a month because of the Olympic Games). That's baaarely enough time to recover from the Giro and be somewhat fresh again for the start of the Tour, but you're still gonna feel the Giro in your legs once the Tour gets to the second/third week. Not only that, you're also at a major disadvantage compared to guys that focused solely on the Tour and have the advantage of a proper training camp at altitude (which both Pogacar and Roglic are doing right now), they've peaked towards the Tour and you're there barely recovered from the Giro. Unless the competition is clearly inferior to you (which is definitely not the case right now with the Slovenians), it's just not achievable anymore imo and it's not something we'll see again in the (near) future. Maybe Pogacar might try it for fun if he has won a few Tours on the bounce but also not before that.
The Giro is an amazing race in its own right but the Tour is the pinnacle of pro cycling so understandably the best riders are focusing solely on that (and most of them have been doing that since the Armstrong days).