When it comes to selecting emails in Gmail Android app to either delete or archive email at once, it doesn't allow that. You have to select each email individually which is itself a frustrating process. Gmail on web allows you to select all emails at once but It's coming to Android Gmail as well. 

With the latest version of Gmail 2023.08.20.561750975.Release, Gmail may allow you to select all emails. I have managed to enable the feature myself and I personally found it very helpful. 

Here is a screen record of the feature in action. 

The main thing to notice here is that Google will select maximum 50 emails at once because there is a limit on Gmail where it fetches a specific number of emails from server in cache. Once the new emails are cached or fetched from servers, you can press "Select all" to select 50 more emails.

But when it comes to unselecting, it will unselect all emails. Like you selected 150 emails, and once you chose "Deselect all", it will unselect all 150 emails not 50. And if you tap "Select all" again after unselecting, it will select all 150 emails not 50. I know it sounds confusing, better look at the video I attached in the article.

Now the final point is - when will it roll out. I am not sure about it because Google do all kind of testing in batches as we all know before rolling out to everyone. 

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