I love it how the name "Google Sandbox" which originated back in 2004 or so, is still around today. So much so that Google year after year has to say there is no Google Sandbox. In short, back in 2004, SEOs noticed that new sites took a while to start to rank well - thus we called it the Google Sandbox, because you had to wait your time to rank well.
That is really no longer the case and I doubt Google called it a "Sandbox" internally. So Google has for years said there is no such thing as the Google Sandbox. The thing is, Matt Cutts somewhat confirmed it existed in terms of how SEOs or webmasters may perceive sites to rank rank well as quickly as they use to. Plus most SEOs felt it did exist when I did a poll about it in 2009.
But yea, just like in 2016, when Gary denied it existed and John Mueller did numerous times, we still have SEOs asking about it.
To ask about the Google Sandbox today seems weird to me. But John Mueller from Google responded on Twitter saying there is no Google Sandbox just the other day.
There is no sandbox.
— 🍌 John 🍌 (@JohnMu) August 19, 2019
Forum discussion at Twitter.