Indeed.
My ownership is proved by my receipt from the store I bought it from.
This vandalization at scale is a CFAA violation. I'd also argue it is a fraudulent sale since not all rights were transferred at sale, and misrepresented a sale instead of an indefinite rental.
And its likely a RICO act, since the C levels and BOD likely knew and/or ordered it.
And damn near everything's wire fraud.
But if anybody does manage to take them to court and win, what would we see? A $10 voucher for the next Oneplus phone? Like we'd buy another.
Their defense would probably be like: "you clicked Yes on the EULA form."
As far as legal arguments go, I imagine their first counter would be that you agreed to the update, so it's on you.