If I have an apple and you agree to buy it for $1T, then the apple is indeed worth $1T at that moment.
After the purchase is complete it is worth ~$0, or whatever the next person is willing to pay you for it.
Alternatively you can say “it is still worth $1T to me” and that would be true as well.
When we are specifically talking about companies, their value is where buyers meet sellers in the order book.
Are you selling me just the apple?
Whether someone else will share your judgment of its worth is highly unlikely, but it is also entirely irrelevant. Worth has never meant "objective value to literally everyone."
I think your definition of value / worth should be based on the seller, not the buyer.
There are contracts that involve exchanging $1 to satisfy some legal requirement of consideration, but the relationship created is worth much more than $1. And of course there are barter transactions where items are exchanged directly without any specific valuation in money involved at all.