You can't make a Gerundiv from an adverbial. That makes no sense because an adverbial does not describe an action. But the Gerundiv does. It tells what has to be done or cannot be done.
Now, if you argue that "schreiben" is not transitive,
Yes, exactly. Let's make it transitive so you can see how the adverbial magically becomes a part of the noun phrase:
Ich schreibe den Text auf das Blatt. – der auf das Blatt zu schreibende Text
So you need an accusative object that becomes the noun of the noun phrase. It does not work with a lone prepositional object either.
Sie wartet auf den Zug. — no Gerundiv possible
That is because that verb has no object that could be the noun of the Gerundiv noun phrase.
If there's both an accusative and a prepositional object, the Gerundiv is about the accusative object:
Er bittet seinen Freund um einen Gefallen. — sein um einen Gefallen zu bittender Freund
For dative verbs, it's extra tricky because the Gerundiv phrase must retain the dative case. So you can only use it as a dative object, dative adverbial, or dative prepositional object.
Er hilft seinem Freund. — Er steht seinem zu helfenden Freund zur Seite. Er bleibt bei seinem zu helfenden Freund. Er erzählt mir von seinem zu helfenden Freund.
And don't mistake adverbial accusatives for accusative objects either:
Er wartet den ganzen Tag auf den Zug. — der ganze auf den Zug zu wartende Tag
While you could build such Gerundiv noun phrases, they are all nonsensical because the adverbial accusative is not the object of that action, as nothing can be done to it. It's a duration during which the action happens. Not its object.
And finally, don't mistake accusative objects for adverbial accusatives:
Sie wartet den ganzen Tag ab. — der ganze abzuwartende Tag
That verb has an event or duration as its accusative object. You can tell that it is an accusative object from the passive voice:
Von ihr wird der ganze Tag abgewartet.
(Yes, you could even say Sie wartet den ganzen Tag den ganzen Tag ab. One is the accusative object, one an adverbial accusative. The Gerundiv noun phrase is der ganze den ganzen Tag abzuwartende Tag.)