If you can afford to keep your phone until you figure out whether a pixel 6 with grapheneos is a good fit for you, I recommend that option. You can then later sell it once you’re more familiar with the new ecosystem.

Otherwise, it’s a bit of a bet. It depends on how confident and familiar you are with privacy compromises, though grapheneos doesn’t force many compromise on you as you can always install the google play services if you need push notifications for WhatsApp for instance (though in that case, I would suggest installing WhatsApp with Google play services in a dedicated separate profile and “pipe” notifications through to your main profile).