I used to have Gmail promotion tab grid view, and today I can't find the way to turn it on, the option is gone. The detail/grid button is gone and I can't find it in the option? Did Google remove the grid view??
'Twould appear to be so.
However, the grid view was a field trial and never "officially" part of the Gmail layout. I guess they decided that it had run its course and was no longer useful, so killed it.
I've not seen any sort of official announcement of its cancellation and, until I saw your question, had forgotten all about it and certainly have seen no other complaints about it online. I don't think it got used much.
That said, the announcement page and sign-up is still available, so maybe you only need to (re-) sign up. https://www.gmail.com/mail/help/fieldtrial.html