Like we covered before, you cannot opt out of Google's mobile-first indexing initiative - it is going to happen with or without you. There is no hiding from it, there is not cheating it, it is coming for you.
Heck, Google's John Mueller made a video just about that question.
John said at the end of the short video "With the longer-term goal of moving all sites over to mobile first indexing, we don't plan to provide an opt-in or opt-out for this kind of indexing."
Forum discussion at Twitter.
