You consent to processing related to keeping you signed in. You don't consent to selling all your data away.
Hm true ToS checkmark is not enough, you need to make the opt-in part clear. But it should be enough to do so when creating a account and for every change. At least if you put a reasonable findable setting page in which allows you to review/change such settings.
But I still believe you can do it once on account creation and then never again if people are logged in and nothing changed.
Apologies if I've misunderstood your claim here but it seems to me that you are saying you can bury consent to processing inside your legalise.
That doesn't comply with the GDPR as I understand it; the consent must be informed and freely given. Informed in that case is debatable since you are lumping a lot of terms together. You certainly can't claim it's freely given if accepting the terms of service is not optional.